icalrecur.c

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/*======================================================================
 FILE: icalrecur.c
 CREATOR: eric 16 May 2000

 SPDX-FileCopyrightText: 2000, Eric Busboom <eric@civicknowledge.com>
 SPDX-License-Identifier: LGPL-2.1-only OR MPL-2.0
========================================================================*/

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include "icalrecur.h"
#include "icalerror_p.h"
#include "icalerror.h"
#include "icallimits.h"
#include "icalmemory.h"
#include "icaltimezone.h"
#include "icalvalue.h" /* for print_date[time]_to_string() */

#include <ctype.h>
#include <stddef.h> /* For offsetof() macro */
#include <stdint.h>
#include <stdlib.h>

#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
#include <pthread.h>
static pthread_mutex_t invalid_rrule_mutex = PTHREAD_MUTEX_INITIALIZER;
#endif

static ICAL_GLOBAL_VAR ical_invalid_rrule_handling invalidRruleHandling = ICAL_RRULE_TREAT_AS_ERROR;

#if defined(HAVE_LIBICU)
#include <unicode/ucal.h>
#include <unicode/ustring.h>
#include <stdbool.h>
#else

/* The maximums below are based on Gregorian leap years */
#undef ICAL_BY_MONTH_SIZE
#undef ICAL_BY_WEEKNO_SIZE
#undef ICAL_BY_YEARDAY_SIZE
#define ICAL_BY_MONTH_SIZE 13    /* 1 to 12 */
#define ICAL_BY_WEEKNO_SIZE 54   /* 1 to 53 */
#define ICAL_BY_YEARDAY_SIZE 367 /* 1 to 366 */
#endif

#if defined(HAVE_LIBICU)
#define MAX_TIME_T_YEAR 20000
#else
#if (SIZEOF_ICALTIME_T > 4)

#define MAX_TIME_T_YEAR 2582
#else

#define MAX_TIME_T_YEAR 2037
#endif
#endif

#define LEAP_MONTH 0x1000

/****************** Forward declarations ******************/
static void icalrecurrencetype_clear(struct icalrecurrencetype *recur);
static short daymask_find_next_bit(const unsigned long *days, short start_index);

/****************** Enumeration Routines ******************/

static const struct freq_map {
    icalrecurrencetype_frequency kind;
    const char str[9];
} freq_map[] = {
    {ICAL_SECONDLY_RECURRENCE, "SECONDLY"},
    {ICAL_MINUTELY_RECURRENCE, "MINUTELY"},
    {ICAL_HOURLY_RECURRENCE, "HOURLY"},
    {ICAL_DAILY_RECURRENCE, "DAILY"},
    {ICAL_WEEKLY_RECURRENCE, "WEEKLY"},
    {ICAL_MONTHLY_RECURRENCE, "MONTHLY"},
    {ICAL_YEARLY_RECURRENCE, "YEARLY"},
    {ICAL_NO_RECURRENCE, ""}};

icalrecurrencetype_frequency icalrecur_string_to_freq(const char *str)
{
    int i;

    for (i = 0; freq_map[i].kind != ICAL_NO_RECURRENCE; i++) {
        if (strcasecmp(str, freq_map[i].str) == 0) {
            return freq_map[i].kind;
        }
    }
    return ICAL_NO_RECURRENCE;
}

const char *icalrecur_freq_to_string(icalrecurrencetype_frequency kind)
{
    int i;

    for (i = 0; freq_map[i].kind != ICAL_NO_RECURRENCE; i++) {
        if (freq_map[i].kind == kind) {
            return freq_map[i].str;
        }
    }
    return 0;
}

static const struct skip_map {
    icalrecurrencetype_skip kind;
    const char str[9];
} skip_map[] = {
    {ICAL_SKIP_BACKWARD, "BACKWARD"},
    {ICAL_SKIP_FORWARD, "FORWARD"},
    {ICAL_SKIP_OMIT, "OMIT"},
    {ICAL_SKIP_UNDEFINED, ""}};

icalrecurrencetype_skip icalrecur_string_to_skip(const char *str)
{
    int i;

    for (i = 0; skip_map[i].kind != ICAL_SKIP_UNDEFINED; i++) {
        if (strcasecmp(str, skip_map[i].str) == 0) {
            return skip_map[i].kind;
        }
    }
    return ICAL_SKIP_UNDEFINED;
}

const char *icalrecur_skip_to_string(icalrecurrencetype_skip kind)
{
    int i;

    for (i = 0; skip_map[i].kind != ICAL_SKIP_UNDEFINED; i++) {
        if (skip_map[i].kind == kind) {
            return skip_map[i].str;
        }
    }
    return 0;
}

static const struct wd_map {
    icalrecurrencetype_weekday wd;
    const char str[3];
} wd_map[] = {
    {ICAL_SUNDAY_WEEKDAY, "SU"},
    {ICAL_MONDAY_WEEKDAY, "MO"},
    {ICAL_TUESDAY_WEEKDAY, "TU"},
    {ICAL_WEDNESDAY_WEEKDAY, "WE"},
    {ICAL_THURSDAY_WEEKDAY, "TH"},
    {ICAL_FRIDAY_WEEKDAY, "FR"},
    {ICAL_SATURDAY_WEEKDAY, "SA"},
    {ICAL_NO_WEEKDAY, ""}};

const char *icalrecur_weekday_to_string(icalrecurrencetype_weekday kind)
{
    int i;

    for (i = 0; wd_map[i].wd != ICAL_NO_WEEKDAY; i++) {
        if (wd_map[i].wd == kind) {
            return wd_map[i].str;
        }
    }

    return 0;
}

icalrecurrencetype_weekday icalrecur_string_to_weekday(const char *str)
{
    int i;

    for (i = 0; wd_map[i].wd != ICAL_NO_WEEKDAY; i++) {
        if (strcasecmp(str, wd_map[i].str) == 0) {
            return wd_map[i].wd;
        }
    }

    return ICAL_NO_WEEKDAY;
}

/*********************** Memory management helper routines ************************/

static void icalrecur_free_by(icalrecurrence_by_data *by)
{
    icalmemory_free_buffer(by->data);
    by->data = NULL;
    by->size = 0;
}

bool icalrecur_resize_by(icalrecurrence_by_data *by, short size)
{
    if (by->size == size) {
        return true;
    }

    if (size == 0) {
        icalrecur_free_by(by);
        return true;
    }

    if ((by->data == NULL) || (by->size == 0)) {
        if ((by->data != NULL) || (by->size != 0)) {
            icalerror_set_errno(ICAL_INTERNAL_ERROR);
            return false;
        }

        by->data = (short *)icalmemory_new_buffer((size_t)size * sizeof(by->data[0]));
        if (!by->data) {
            return false;
        }
    } else {
        short *new_data = (short *)icalmemory_resize_buffer(by->data, (size_t)size * sizeof(by->data[0]));
        if (!new_data) {
            return false;
        }

        by->data = new_data;
    }

    if (size > by->size) {
        memset(&by->data[by->size], 0, (size_t)(size - by->size) * sizeof(by->data[0]));
    }

    by->size = size;

    return true;
}

/*********************** Rule parsing routines ************************/

struct icalrecur_parser {
    const char *rule;
    char *copy;
    char *this_clause;
    char *next_clause;

    struct icalrecurrencetype *rt;
};

enum expand_table
{
    UNKNOWN = 0,
    CONTRACT = 1,
    EXPAND = 2,
    ILLEGAL = 3
};

struct expand_split_map_struct {
    icalrecurrencetype_frequency frequency;

    /* Elements of the 'map' array correspond to the BYxxx rules:
       Second,Minute,Hour,Day,Month Day,Year Day,Week No,Month,SetPos */

    short map[ICAL_BY_NUM_PARTS];
};

static const struct expand_split_map_struct expand_map[] = {
    /*                           M  W  YD MD D  h  m  s  P */
    {ICAL_SECONDLY_RECURRENCE, {1, 3, 1, 1, 1, 1, 1, 1, 1}},
    {ICAL_MINUTELY_RECURRENCE, {1, 3, 1, 1, 1, 1, 1, 2, 1}},
    {ICAL_HOURLY_RECURRENCE, {1, 3, 1, 1, 1, 1, 2, 2, 1}},
    {ICAL_DAILY_RECURRENCE, {1, 3, 3, 1, 1, 2, 2, 2, 1}},
    {ICAL_WEEKLY_RECURRENCE, {1, 3, 3, 3, 2, 2, 2, 2, 1}},
    {ICAL_MONTHLY_RECURRENCE, {1, 3, 3, 2, 2, 2, 2, 2, 1}},
    {ICAL_YEARLY_RECURRENCE, {2, 2, 2, 2, 2, 2, 2, 2, 1}},
    {ICAL_NO_RECURRENCE, {0, 0, 0, 0, 0, 0, 0, 0, 0}}};

static const struct recur_map {
    const char *str;
    int size;
    int min;
    int isTime;
} recur_map[] = {
    {"BYMONTH", ICAL_BY_MONTH_SIZE, 1, 0},
    {"BYWEEKNO", ICAL_BY_WEEKNO_SIZE, -1, 0},
    {"BYYEARDAY", ICAL_BY_YEARDAY_SIZE, -1, 0},
    {"BYMONTHDAY", ICAL_BY_MONTHDAY_SIZE, -1, 0},
    {"BYDAY", ICAL_BY_DAY_SIZE, 0, 0},
    {"BYHOUR", ICAL_BY_HOUR_SIZE, 0, 1},
    {"BYMINUTE", ICAL_BY_MINUTE_SIZE, 0, 1},
    {"BYSECOND", ICAL_BY_SECOND_SIZE, 0, 1},
    {"BYSETPOS", ICAL_BY_SETPOS_SIZE, -1, 0},
};

static const char *icalrecur_first_clause(struct icalrecur_parser *parser)
{
    char *idx;

    parser->this_clause = parser->copy;

    idx = strchr(parser->this_clause, ';');

    if (idx == 0) {
        parser->next_clause = 0;
        return 0;
    }

    *idx = 0;
    idx++;
    parser->next_clause = idx;

    return parser->this_clause;
}

static const char *icalrecur_next_clause(struct icalrecur_parser *parser)
{
    char *idx;

    parser->this_clause = parser->next_clause;

    if (parser->this_clause == 0) {
        return 0;
    }

    idx = strchr(parser->this_clause, ';');

    if (idx == 0) {
        parser->next_clause = 0;
    } else {
        *idx = 0;
        idx++;
        parser->next_clause = idx;
    }

    return parser->this_clause;
}

static void icalrecur_clause_name_and_value(struct icalrecur_parser *parser,
                                            char **name, char **value)
{
    char *idx;

    *name = parser->this_clause;

    idx = strchr(parser->this_clause, '=');

    if (idx == 0) {
        *name = 0;
        *value = 0;
        return;
    }

    *idx = 0;
    idx++;
    *value = idx;
}

/*
 * We expect BYHOUR, BYMINUTE, and BYSECOND data to be sorted.
 */
static void sort_byrules(icalrecurrence_by_data *by)
{
    short *array = by->data;

    int i, j;

    for (i = 1; i < by->size; i++) {
        for (j = i - 1; j >= 0 && array[j] > array[j + 1]; j--) {
            short tmp = array[j + 1];

            array[j + 1] = array[j];
            array[j] = tmp;
        }
    }
}

/*
 * Sort BYSETPOS list in ascending order of magnitude,
 * with negatives after positives
 */
static void sort_bysetpos(icalrecurrence_by_data *by)
{
#define SIGN(A) ((A) < 0 ? -1 : 1)
    short *array = by->data;

    int i, j;

    for (i = 1; i < by->size; i++) {
        for (j = i - 1;
             j >= 0 && ((SIGN(array[j]) == SIGN(array[j + 1]) && abs(array[j]) > abs(array[j + 1])) ||
                        (array[j] < 0 && array[j + 1] > 0));
             j--) {
            short tmp = array[j + 1];

            array[j + 1] = array[j];
            array[j] = tmp;
        }
    }
#undef SIGN
}

/* returns < 0 if a parsing problem:
   -2 if an RSCALE rule is encountered yet we don't RSCALE support enabled
   -1 for all other parsing problems
*/
static int icalrecur_add_byrules(const struct icalrecur_parser *parser, icalrecurrence_by_data *by,
                                 int min, int size, char *vals)
{
    char *t, *n;
    int i = 0;
    int max = size - (min == 0);

    n = vals;

    if (!icalrecur_resize_by(by, size)) {
        return -1;
    }

    while (n != 0) {
        if (i == size) {
            return -1;
        }

        t = n;

        n = strchr(t, ',');

        if (n != 0) {
            *n = 0;
            n++;
        }

        // empty string is not allowed here
        if (!*t) {
            return -1;
        }

        char *t_end;
        int v = strtol(t, &t_end, 10);

        // We check for parsing errors later, but not if the string ends with 'L',
        // so explicitly check the value here.
        if (t == t_end) {
            return -1;
        }
        t = t_end;

        /* Sanity check value */
        if (v < 0) {
            if (min >= 0 || v <= -max) {
                return -1;
            }
        } else if (v > 0) {
            if (v >= max) {
                return -1;
            }
        } else if (min) {
            return -1;
        }

        if (*t) {
            /* Check for leap month suffix (RSCALE only) */
            if (by == &parser->rt->by[ICAL_BY_MONTH] && strcmp(t, "L") == 0) {
                /* The "L" suffix in a BYMONTH recur-rule-part
                    is encoded by setting a high-order bit */
                v |= LEAP_MONTH;
            } else {
                return -1;
            }
        }

        by->data[i++] = (short)v;
    }

    if (!icalrecur_resize_by(by, i)) {
        return -1;
    }

    /* Sort time bylists.
     * Date bylists do not require sorting because they are implemented
     * differently (with a bitmask), and are not directly used to find
     * the next occurrence.
     */
    if (by == &parser->rt->by[ICAL_BY_HOUR] ||
        by == &parser->rt->by[ICAL_BY_MINUTE] ||
        by == &parser->rt->by[ICAL_BY_SECOND]) {
        sort_byrules(by);
    }
    /* BYSETPOS is sorted specially */
    else if (by == &parser->rt->by[ICAL_BY_SET_POS]) {
        sort_bysetpos(by);
    }

    return 0;
}

/*
 * Days in the BYDAY rule are expected by the code to be sorted, and while
 * this may be the common case, the RFC doesn't actually mandate it. This
 * function sorts the days taking into account the first day of week.
 */
static void sort_bydayrules(struct icalrecur_parser *parser)
{
    icalrecurrence_by_data *by = &parser->rt->by[ICAL_BY_DAY];
    short *array = by->data;

    int week_start, i, j;

    week_start = (int)parser->rt->week_start;

    for (i = 0; i < by->size; i++) {
        for (j = 0; j < i; j++) {
            int one = (int)icalrecurrencetype_day_day_of_week(array[j]) - week_start;
            if (one < 0) {
                one += 7;
            }
            int two = (int)icalrecurrencetype_day_day_of_week(array[i]) - week_start;
            if (two < 0) {
                two += 7;
            }

            if (one > two) {
                short tmp = array[j];

                array[j] = array[i];
                array[i] = tmp;
            }
        }
    }
}

static int icalrecur_add_bydayrules(struct icalrecur_parser *parser,
                                    const char *vals)
{
    char *t, *n;
    icalrecurrence_by_data *by = &parser->rt->by[ICAL_BY_DAY];

    char *vals_copy;
    int idx = 0;

    if (!icalrecur_resize_by(by, ICAL_BY_DAY_SIZE)) {
        return -1;
    }

    vals_copy = icalmemory_strdup(vals);
    n = vals_copy;

    while (n != 0) {
        int sign = 1;
        signed char weekno;
        icalrecurrencetype_weekday wd;

        if (idx >= by->size) {
            icalmemory_free_buffer(vals_copy);
            return -1;
        }

        t = n;

        n = strchr(t, ',');

        if (n != 0) {
            *n = 0;
            n++;
        }

        // empty string is not allowed here
        if (!t[0]) {
            icalmemory_free_buffer(vals_copy);
            return -1;
        }

        /* Get Optional weekno */
        char *t_end;
        long tmpl = strtol(t, &t_end, 10);
        weekno = (signed char)tmpl;

        // overflow?
        /* cppcheck-suppress knownConditionTrueFalse */
        if (weekno != tmpl) {
            icalmemory_free_buffer(vals_copy);
            return -1;
        }

        // WeekNo 0 doesn't exist
        if ((weekno == 0) && (t != t_end)) {
            icalmemory_free_buffer(vals_copy);
            return -1;
        }
        t = t_end;

        if (weekno < 0) {
            weekno = -weekno;
            sign = -1;
        }

        /* Outlook/Exchange generate "BYDAY=MO, FR" and "BYDAY=2 TH".
         * Cope with that.
         */
        if (*t == ' ') {
            t++;
        }

        wd = icalrecur_string_to_weekday(t);

        /* Sanity check value */
        if (wd == ICAL_NO_WEEKDAY || weekno >= ICAL_BY_WEEKNO_SIZE) {
            icalmemory_free_buffer(vals_copy);
            return -1;
        }

        by->data[idx++] = icalrecurrencetype_encode_day(wd, sign * weekno);
    }

    icalmemory_free_buffer(vals_copy);

    if (!icalrecur_resize_by(by, idx)) {
        return -1;
    }

    sort_bydayrules(parser);

    return 0;
}

struct icalrecurrencetype *icalrecurrencetype_new(void)
{
    struct icalrecurrencetype *rule;

    rule = (struct icalrecurrencetype *)icalmemory_new_buffer(sizeof(*rule));

    if (!rule) {
        return NULL;
    }

    memset(rule, 0, sizeof(*rule));
    rule->refcount = 1;
    icalrecurrencetype_clear(rule);

    return rule;
}

static void icalrecurrencetype_free(struct icalrecurrencetype *recur, int free_self)
{
#define SAFEFREE(p)                \
    if (p) {                       \
        icalmemory_free_buffer(p); \
        (p) = 0;                   \
    }

    SAFEFREE(recur->rscale);
    for (int i = 0; i < ICAL_BY_NUM_PARTS; i++) {
        SAFEFREE(recur->by[i].data);
    }

#undef SAFEFREE

    if (free_self) {
        icalmemory_free_buffer(recur);
    }
}

void icalrecurrencetype_ref(struct icalrecurrencetype *recur)
{
    icalerror_check_arg_rv((recur != NULL), "recur");
    icalerror_check_arg_rv((recur->refcount > 0), "recur->refcount > 0");

    recur->refcount++;
}

void icalrecurrencetype_unref(struct icalrecurrencetype *recur)
{
    icalerror_check_arg_rv((recur != NULL), "recur");
    icalerror_check_arg_rv((recur->refcount > 0), "recur->refcount > 0");

    recur->refcount--;

    if (recur->refcount != 0) {
        return;
    }

    icalrecurrencetype_free(recur, 1);
}

static void *icalrecur_memdup(void *p, size_t size, int *error)
{
    if ((p == NULL) || (size == 0)) {
        return p;
    }

    void *newp = icalmemory_new_buffer(size);
    if (newp) {
        memcpy(newp, p, size);
    } else {
        *error = 1;
    }

    return newp;
}

static icalrecurrence_by_data icalrecur_by_dup(icalrecurrence_by_data *by, int *error)
{
    icalrecurrence_by_data newby = {0, 0};

    newby.data = icalrecur_memdup(by->data, (size_t)by->size * sizeof(by->data[0]), error);
    if (newby.data) {
        newby.size = by->size;
    }

    return newby;
}

struct icalrecurrencetype *icalrecurrencetype_clone(struct icalrecurrencetype *recur)
{
    struct icalrecurrencetype *res;
    int error = 0;

    icalerror_check_arg_rz((recur != NULL), "recur");

    res = icalrecurrencetype_new();
    if (!res) {
        return NULL;
    }

    memcpy(res, recur, sizeof(*res));

    res->refcount = 1;

    if (res->rscale) {
        res->rscale = icalmemory_strdup(res->rscale);
        if (!res->rscale) {
            error = 1;
        }
    }

    for (int i = 0; i < ICAL_BY_NUM_PARTS; i++) {
        icalrecurrence_by_data *src_by = &recur->by[i];
        icalrecurrence_by_data *dst_by = &res->by[i];
        *dst_by = icalrecur_by_dup(src_by, &error);
    }

    if (error) {
        icalrecurrencetype_free(res, 1);
        return NULL;
    }

    return res;
}

struct icalrecurrencetype *icalrecurrencetype_new_from_string(const char *str)
{
    struct icalrecur_parser parser = {0};
    icalrecurrencetype_byrule byrule;

    icalerror_check_arg_re(str != 0, "str", 0);

    parser.rt = icalrecurrencetype_new();
    if (!parser.rt) {
        return NULL;
    }

    /* Set up the parser struct */
    parser.rule = str;
    parser.copy = icalmemory_strdup(parser.rule);
    parser.this_clause = parser.copy;

    if (parser.copy == 0) {
        icalerror_set_errno(ICAL_NEWFAILED_ERROR);
        icalrecurrencetype_unref(parser.rt);
        return NULL;
    }

    /* Loop through all of the clauses */
    for (icalrecur_first_clause(&parser);
         parser.this_clause != 0; icalrecur_next_clause(&parser)) {
        char *name, *value;
        int r = 0;

        icalrecur_clause_name_and_value(&parser, &name, &value);

        if (name == 0) {
            if (strlen(parser.this_clause) > 0) {
                r = -1;
            } else {
                /* Hit an empty name/value pair,
                   but we're also at the end of the string.
                   This was probably a trailing semicolon with no data
                   (e.g. "FREQ=WEEKLY;INTERVAL=1;BYDAY=MO;")
                */
                break;
            }
        } else if (strcasecmp(name, "FREQ") == 0) {
            if (parser.rt->freq != ICAL_NO_RECURRENCE) {
                /* Don't allow multiple FREQs */
                r = -1;
            } else {
                parser.rt->freq = icalrecur_string_to_freq(value);
                if (parser.rt->freq == ICAL_NO_RECURRENCE) {
                    r = -1;
                }
            }
        } else if (strcasecmp(name, "RSCALE") == 0) {
            if (parser.rt->rscale != NULL) {
                /* Don't allow multiple RSCALEs */
                r = -1;
            } else {
                parser.rt->rscale = icalmemory_strdup(value);
            }
        } else if (strcasecmp(name, "SKIP") == 0) {
            if (parser.rt->skip != ICAL_SKIP_OMIT) {
                /* Don't allow multiple SKIPs */
                r = -1;
            } else {
                parser.rt->skip = icalrecur_string_to_skip(value);
                if (parser.rt->skip == ICAL_SKIP_UNDEFINED) {
                    r = -1;
                }
            }
        } else if (strcasecmp(name, "COUNT") == 0) {
            if (parser.rt->count > 0 || !icaltime_is_null_time(parser.rt->until)) {
                /* Don't allow multiple COUNTs, or both COUNT and UNTIL */
                r = -1;
            } else {
                parser.rt->count = atoi(value);
                /* don't allow count to be less than 1 */
                if (parser.rt->count < 1) {
                    r = -1;
                }
            }
        } else if (strcasecmp(name, "UNTIL") == 0) {
            if (parser.rt->count > 0 || !icaltime_is_null_time(parser.rt->until)) {
                /* Don't allow multiple COUNTs, or both COUNT and UNTIL */
                r = -1;
            } else {
                parser.rt->until = icaltime_from_string(value);
                if (icaltime_is_null_time(parser.rt->until)) {
                    r = -1;
                }
            }
        } else if (strcasecmp(name, "INTERVAL") == 0) {
            if (parser.rt->interval > 1) {
                /* Don't allow multiple INTERVALs */
                r = -1;
            } else {
                int tmp = atoi(value);
                parser.rt->interval = (short)tmp;

                // overflow?
                /* cppcheck-suppress knownConditionTrueFalse */
                if (parser.rt->interval != tmp) {
                    r = -1;
                }

                /* don't allow an interval to be less than 1
                   (RFC specifies an interval must be a positive integer) */
                if (parser.rt->interval < 1) {
                    r = -1;
                }
            }
        } else if (strcasecmp(name, "WKST") == 0) {
            if (parser.rt->week_start != ICAL_MONDAY_WEEKDAY) {
                /* Don't allow multiple WKSTs */
                r = -1;
            } else {
                parser.rt->week_start = icalrecur_string_to_weekday(value);
                if (parser.rt->week_start == ICAL_NO_WEEKDAY) {
                    r = -1;
                } else {
                    sort_bydayrules(&parser);
                }
            }
        } else if (strncasecmp(name, "BY", 2) == 0) {
            r = -1;

            for (byrule = 0; byrule < ICAL_BY_NUM_PARTS; ++byrule) {
                if (strcasecmp(name + 2, recur_map[byrule].str + 2) == 0) {
                    if (byrule == ICAL_BY_DAY) {
                        r = icalrecur_add_bydayrules(&parser, value);
                    } else {
                        icalrecurrence_by_data *by = &parser.rt->by[byrule];
                        r = icalrecur_add_byrules(&parser, by,
                                                  recur_map[byrule].min,
                                                  recur_map[byrule].size,
                                                  value);
                    }
                    break;
                }
            }
        } else {
            r = -1;
        }

        if (r) {
            /* Note: silently ignore when we have a leap month, yet don't have RSCALE support.
               The magic value "-2" indicates when that happens.
            */
            if (r != -2) {
                icalerror_set_errno(ICAL_MALFORMEDDATA_ERROR);
            }
            icalrecurrencetype_clear(parser.rt);
            break;
        }
    }

    for (byrule = 0; byrule < ICAL_BY_NUM_PARTS; ++byrule) {
        icalrecurrence_by_data *by = &parser.rt->by[byrule];

        if (by->size > 0 &&
            expand_map[parser.rt->freq].map[byrule] == ILLEGAL) {
            ical_invalid_rrule_handling rruleHandlingSetting =
                ical_get_invalid_rrule_handling_setting();

            if (rruleHandlingSetting == ICAL_RRULE_TREAT_AS_ERROR) {
                icalerror_set_errno(ICAL_MALFORMEDDATA_ERROR);
                icalrecurrencetype_clear(parser.rt);
                break;
            } else {
                icalrecur_free_by(by);
            }
        }
    }

    icalmemory_free_buffer(parser.copy);

    if (parser.rt->freq == ICAL_NO_RECURRENCE) {
        icalrecurrencetype_unref(parser.rt);
        parser.rt = NULL;
    }

    return parser.rt;
}

char *icalrecurrencetype_as_string(struct icalrecurrencetype *recur)
{
    char *buf;

    buf = icalrecurrencetype_as_string_r(recur);
    icalmemory_add_tmp_buffer(buf);
    return buf;
}

char *icalrecurrencetype_as_string_r(struct icalrecurrencetype *recur)
{
    char *str;
    char *str_p;
    size_t buf_sz = 200;
    char temp[20] = {0};
    int i, j;

    if (recur == 0 || recur->freq == ICAL_NO_RECURRENCE) {
        return 0;
    }

    str = (char *)icalmemory_new_buffer(buf_sz);
    str_p = str;

    if (recur->rscale != 0) {
        icalmemory_append_string(&str, &str_p, &buf_sz, "RSCALE=");
        icalmemory_append_string(&str, &str_p, &buf_sz, recur->rscale);

        /* Omit is the default, so no need to write that out */
        if (recur->skip != ICAL_SKIP_OMIT) {
            const char *skipstr = icalrecur_skip_to_string(recur->skip);
            icalmemory_append_string(&str, &str_p, &buf_sz, ";SKIP=");
            icalmemory_append_string(&str, &str_p, &buf_sz, skipstr);
        }
        icalmemory_append_char(&str, &str_p, &buf_sz, ';');
    }

    icalmemory_append_string(&str, &str_p, &buf_sz, "FREQ=");
    icalmemory_append_string(&str, &str_p, &buf_sz,
                             icalrecur_freq_to_string(recur->freq));

    /* 1 is the default, so no need to write that out */
    if (recur->interval != 1) {
        snprintf(temp, sizeof(temp), "%d", recur->interval);
        icalmemory_append_string(&str, &str_p, &buf_sz, ";INTERVAL=");
        icalmemory_append_string(&str, &str_p, &buf_sz, temp);
    }

    /* Monday is the default, so no need to write that out */
    if (recur->week_start != ICAL_MONDAY_WEEKDAY &&
        recur->week_start != ICAL_NO_WEEKDAY) {
        int dow = (int)icalrecurrencetype_day_day_of_week(recur->week_start);
        const char *daystr = icalrecur_weekday_to_string((enum icalrecurrencetype_weekday)dow);
        icalmemory_append_string(&str, &str_p, &buf_sz, ";WKST=");
        icalmemory_append_string(&str, &str_p, &buf_sz, daystr);
    }

    for (j = 0; j < ICAL_BY_NUM_PARTS; j++) {
        const icalrecurrence_by_data *by = &recur->by[j];

        /* Skip unused arrays */
        if (by->size > 0) {
            icalmemory_append_char(&str, &str_p, &buf_sz, ';');
            icalmemory_append_string(&str, &str_p, &buf_sz, recur_map[j].str);
            icalmemory_append_char(&str, &str_p, &buf_sz, '=');

            int limit = recur_map[j].size - 1;
            for (i = 0; i < limit && i < by->size; i++) {
                if (j == ICAL_BY_DAY) {
                    int pos = icalrecurrencetype_day_position(by->data[i]);
                    int dow = (int)icalrecurrencetype_day_day_of_week(by->data[i]);
                    const char *daystr = icalrecur_weekday_to_string((enum icalrecurrencetype_weekday)dow);

                    if (pos == 0) {
                        icalmemory_append_string(&str, &str_p, &buf_sz, daystr);
                    } else {
                        snprintf(temp, sizeof(temp), "%d%s", pos, daystr);
                        icalmemory_append_string(&str, &str_p, &buf_sz, temp);
                    }

                } else if (j == ICAL_BY_MONTH &&
                           icalrecurrencetype_month_is_leap(by->data[i])) {
                    snprintf(temp, sizeof(temp), "%dL",
                             icalrecurrencetype_month_month(by->data[i]));
                    icalmemory_append_string(&str, &str_p, &buf_sz, temp);
                } else {
                    snprintf(temp, sizeof(temp), "%d", by->data[i]);
                    icalmemory_append_string(&str, &str_p, &buf_sz, temp);
                }

                if ((i + 1) < limit && by->size > i + 1) {
                    icalmemory_append_char(&str, &str_p, &buf_sz, ',');
                }
            }
        }
    }

    if (recur->until.year != 0) {
        temp[0] = 0;
        if (recur->until.is_date) {
            print_date_to_string(temp, &(recur->until));
        } else {
            print_datetime_to_string(temp, &(recur->until));
        }

        icalmemory_append_string(&str, &str_p, &buf_sz, ";UNTIL=");
        icalmemory_append_string(&str, &str_p, &buf_sz, temp);
    }

    else if (recur->count != 0) {
        snprintf(temp, sizeof(temp), "%d", recur->count);
        icalmemory_append_string(&str, &str_p, &buf_sz, ";COUNT=");
        icalmemory_append_string(&str, &str_p, &buf_sz, temp);
    }

    return str;
}

/************************* occurrence iteration routines ******************/

/* Number of bits in an unsigned long */
#define BITS_PER_LONG ((unsigned short)(8 * sizeof(unsigned long)))

/* Number of longs in mask of n bits */
#define LONGS_PER_BITS(n) (((n) + BITS_PER_LONG - 1) / BITS_PER_LONG)

#define ICAL_YEARDAYS_MASK_SIZE (ICAL_BY_YEARDAY_SIZE + 7)
#define ICAL_YEARDAYS_MASK_OFFSET 4

typedef struct icalrecurrence_iterator_by_data {
    icalrecurrence_by_data by;
    short index;
    short orig_data;

    // Static buffer for BY values that need to be modified by the iterator, so we don't modify the rule.
    // We have one value for each BY rule.
    short buffer_value;
} icalrecurrence_iterator_by_data;

struct icalrecur_iterator_impl {
    struct icaltimetype dtstart;     /* copy of DTSTART: to fill in defaults */
    struct icalrecurrencetype *rule; /* reference to RRULE */

    struct icaltimetype rstart; /* DTSTART in RSCALE  */
    struct icaltimetype istart; /* Gregorian start time for iterator */
    struct icaltimetype iend;   /* Gregorian end time for iterator */
    struct icaltimetype last;   /* last time returned from iterator */
    int32_t occurrence_no;      /* number of steps made on the iterator */

    int32_t set_pos;             /* our position in the recurrence set */
    int32_t recurrence_set_size; /* the size of the recurrence set */
    short sp_idxp, sp_idxn;      /* positive and negative BYSETPOS indices */
    short sp_pmax;               /* the last index of the BYSETPOS array with a positive value */

#if defined(HAVE_LIBICU)
    UCalendar *greg;   /* Gregorian calendar */
    UCalendar *rscale; /* RSCALE calendar    */
#endif

    struct icaltimetype period_start; /* Start date of monthly/yearly period */

    /* days[] is a bitmask of year days.  A bit value of 1 marks an occurrence.
       The size of the bitmask is 7 + max days in year to accommodate full first
       and last weeks of the year: up to 3 days in previous year and
       up to 4 days in following year.  As a result, the days are offset by 4:
       bit 0 is day -3 (3rd last day of previous year) and bit 4 is day 1
       of the current year.  Days in the following year use higher day numbers,
       e.g. day 367 is day 1 or 2 of following year depending on whether the
       current year is a leap year.

       days_index is the day of year of the next occurrence,
       with a range of -3 to 4 + days in year.
    */
    unsigned long days[LONGS_PER_BITS(ICAL_YEARDAYS_MASK_SIZE)];
    short days_index;

    icalrecurrencetype_byrule byrule;
    icalrecurrence_iterator_by_data bydata[ICAL_BY_NUM_PARTS];
};

static void daysmask_clearall(unsigned long mask[])
{
    memset(mask, 0,
           sizeof(unsigned long) * LONGS_PER_BITS(ICAL_YEARDAYS_MASK_SIZE));
}

static void daysmask_set_range(unsigned long days[], int fromDayIncl, int untilDayExcl, int v)
{
    int fromBitIdx = fromDayIncl + ICAL_YEARDAYS_MASK_OFFSET;
    int untilBitIdx = untilDayExcl + ICAL_YEARDAYS_MASK_OFFSET;

    for (int word_idx = fromBitIdx / BITS_PER_LONG;
         word_idx < (int)((untilBitIdx + BITS_PER_LONG - 1) / BITS_PER_LONG);
         word_idx++) {
        int lowerBitIdxIncl = (fromBitIdx <= (int)(word_idx * BITS_PER_LONG))
                                  ? 0
                                  : (fromBitIdx - (int)(word_idx * BITS_PER_LONG));
        int upperBitIdxExcl = (untilBitIdx >= (int)((word_idx + 1) * BITS_PER_LONG))
                                  ? (int)BITS_PER_LONG
                                  : (int)(untilBitIdx - (int)(word_idx * BITS_PER_LONG));

        unsigned long mask = (unsigned long)-1;
        if (lowerBitIdxIncl > 0) {
            mask &= ((unsigned long)-1) << lowerBitIdxIncl;
        }
        if (upperBitIdxExcl < (int)BITS_PER_LONG) {
            mask &= ((unsigned long)-1) >> (BITS_PER_LONG - upperBitIdxExcl);
        }

        if (v) {
            days[word_idx] |= mask;
        } else {
            days[word_idx] &= ~mask;
        }
    }
}

static int daysmask_setbit(unsigned long mask[], short n, int v)
{
    int prev;

    n += ICAL_YEARDAYS_MASK_OFFSET;

    if (n >= 0) {
        prev = (mask[n / BITS_PER_LONG] & (1UL << (n % BITS_PER_LONG))) ? 1 : 0;
    } else {
        prev = (mask[n / BITS_PER_LONG] & (1UL >> (-n % BITS_PER_LONG))) ? 1 : 0;
    }
    if (v != prev) {
        if (v) {
            if (n >= 0) {
                mask[n / BITS_PER_LONG] |= (1UL << (n % BITS_PER_LONG));
            } else {
                mask[n / BITS_PER_LONG] |= (1UL >> (-n % BITS_PER_LONG));
            }
        } else {
            if (n >= 0) {
                mask[n / BITS_PER_LONG] &= ~(1UL << (n % BITS_PER_LONG));
            } else {
                mask[n / BITS_PER_LONG] &= ~(1UL >> (-n % BITS_PER_LONG));
            }
        }
    }

    return prev;
}

static unsigned long daysmask_getbit(const unsigned long mask[], short n)
{
    n += ICAL_YEARDAYS_MASK_OFFSET;
    return (mask[n / BITS_PER_LONG] >> (n % BITS_PER_LONG)) & 1;
}

static bool has_by_data(icalrecur_iterator *impl, icalrecurrencetype_byrule byrule)
{
    return (impl->bydata[byrule].orig_data == 1);
}

static void recur_iterator_set_static_single_by_value(icalrecur_iterator *impl,
                                                      icalrecurrencetype_byrule byrule, short value)
{
    icalrecurrence_iterator_by_data *by = &impl->bydata[byrule];
    by->by.size = 1;
    by->by.data = &by->buffer_value;
    by->by.data[0] = value;
}

static void setup_defaults(icalrecur_iterator *impl,
                           icalrecurrencetype_byrule byrule, int deftime)
{
    icalrecurrencetype_frequency freq = impl->rule->freq;

    if (impl->dtstart.is_date && recur_map[byrule].isTime) {
        // The BYSECOND, BYMINUTE and BYHOUR rule parts MUST NOT be specified
        // when the associated "DTSTART" property has a DATE value type.
        // These rule parts MUST be ignored in RECUR value that violate the
        // above requirement (e.g., generated by applications that pre-date
        // this revision of iCalendar).
        recur_iterator_set_static_single_by_value(impl, byrule, 0);
    } else if (expand_map[freq].map[byrule] == EXPAND) {
        /* Re-write the BY rule arrays with data from the DTSTART time so
           we don't have to explicitly deal with DTSTART */
        if (impl->bydata[byrule].by.size == 0) {
            recur_iterator_set_static_single_by_value(impl, byrule, (short)deftime);
        }
    }
}

static int weeks_in_year(int year)
{
    /* Long years occur when year starts on Thu or leap year starts on Wed */
    int dow = icaltime_day_of_week(icaltime_from_day_of_year(1, year));
    int is_long = (dow == 5 || (dow == 4 && icaltime_is_leap_year(year)));

    return (52 + is_long);
}

static int __greg_month_diff(icaltimetype a, icaltimetype b)
{
    return (12 * (b.year - a.year) + (b.month - a.month));
}

static void __get_start_time(icalrecur_iterator *impl, icaltimetype date,
                             int *hour, int *minute, int *second)
{
    icalrecurrencetype_frequency freq = impl->rule->freq;

    if (freq == ICAL_HOURLY_RECURRENCE) {
        *hour = date.hour;
    } else if (has_by_data(impl, ICAL_BY_HOUR)) {
        *hour = impl->bydata[ICAL_BY_HOUR].by.data[0];
    } else {
        *hour = impl->rstart.hour;
    }

    if (freq == ICAL_MINUTELY_RECURRENCE) {
        *minute = date.minute;
    } else if (has_by_data(impl, ICAL_BY_MINUTE)) {
        *minute = impl->bydata[ICAL_BY_MINUTE].by.data[0];
    } else {
        *minute = impl->rstart.minute;
    }

    if (freq == ICAL_SECONDLY_RECURRENCE) {
        *second = date.second;
    } else if (has_by_data(impl, ICAL_BY_SECOND)) {
        *second = impl->bydata[ICAL_BY_SECOND].by.data[0];
    } else {
        *second = impl->rstart.second;
    }
}

static int __day_diff(icalrecur_iterator *impl, icaltimetype a, icaltimetype b);

#if defined(HAVE_LIBICU)
/*
 * Callbacks for recurrence rules with RSCALE support (using ICU)
 *
 * References:
 *   - tools.ietf.org/html/rfc7529
 *   - en.wikipedia.org/wiki/Intercalation_%28timekeeping%29
 *   - icu-project.org/apiref/icu4c/ucal_8h.html
 *   - cldr.unicode.org/development/development-process/design-proposals/chinese-calendar-support
 *   - cldr.unicode.org/development/development-process/design-proposals/islamic-calendar-types
 *
 * ICU Notes:
 *   - Months are 0-based
 *   - Leap months in Chinese and Hebrew calendars are handled differently
 */

icalarray *icalrecurrencetype_rscale_supported_calendars(void)
{
    UErrorCode status = U_ZERO_ERROR;
    UEnumeration *en;
    icalarray *calendars;
    const char *cal;

    calendars = icalarray_new(sizeof(const char **), 20);

    en = ucal_getKeywordValuesForLocale("calendar", "", false, &status);
    while ((cal = uenum_next(en, NULL, &status))) {
        cal = icalmemory_tmp_copy(cal);
        icalarray_append(calendars, (const void *)&cal);
    }
    uenum_close(en);

    return calendars;
}

static void set_second(icalrecur_iterator *impl, int second)
{
    ucal_set(impl->rscale, UCAL_SECOND, (int32_t)second);
}

static void set_minute(icalrecur_iterator *impl, int minute)
{
    ucal_set(impl->rscale, UCAL_MINUTE, (int32_t)minute);
}

static void set_hour(icalrecur_iterator *impl, int hour)
{
    ucal_set(impl->rscale, UCAL_HOUR_OF_DAY, (int32_t)hour);
}

static void __set_month(icalrecur_iterator *impl, int month)
{
    bool is_leap_month = icalrecurrencetype_month_is_leap(month);

    month = icalrecurrencetype_month_month(month) - 1; /* UCal is 0-based */

    ucal_set(impl->rscale, UCAL_MONTH, (int32_t)month);
    if (is_leap_month) {
        ucal_set(impl->rscale, UCAL_IS_LEAP_MONTH, 1);
    }
}

static int set_month(icalrecur_iterator *impl, int month)
{
    UErrorCode status = U_ZERO_ERROR;
    int actual_month;

    __set_month(impl, month);

    ucal_set(impl->rscale, UCAL_DAY_OF_MONTH, (int32_t)1);

    actual_month = 1 + /* UCal is 0-based */
                   (int)ucal_get(impl->rscale, UCAL_MONTH, &status);

    if (ucal_get(impl->rscale, UCAL_IS_LEAP_MONTH, &status)) {
        actual_month |= LEAP_MONTH;
    }

    if (actual_month != month) {
        switch (impl->rule->skip) {
        default:
            /* Should never get here! */

        case ICAL_SKIP_OMIT:
            /* Invalid month */
            return 0;

        case ICAL_SKIP_BACKWARD:
            /* Skip back to next valid month */
            ucal_add(impl->rscale, UCAL_MONTH, (int32_t)-1, &status);
            break;

        case ICAL_SKIP_FORWARD:
            /* UCal skips forward to valid month by default */
            break;
        }
    }

    return (1 + /* UCal is 0-based */
            (int)ucal_get(impl->rscale, UCAL_MONTH, &status));
}

static int get_months_in_year(icalrecur_iterator *impl, int year)
{
    UErrorCode status = U_ZERO_ERROR;

    if (year) {
        ucal_set(impl->rscale, UCAL_YEAR, (int32_t)year);
    }

    return (1 + /* UCal is 0-based */
            (int)ucal_getLimit(impl->rscale, UCAL_MONTH,
                               UCAL_ACTUAL_MAXIMUM, &status));
}

static int get_days_in_year(icalrecur_iterator *impl, int year)
{
    UErrorCode status = U_ZERO_ERROR;

    if (year) {
        ucal_set(impl->rscale, UCAL_YEAR, (int32_t)year);
    }

    return (int)ucal_getLimit(impl->rscale, UCAL_DAY_OF_YEAR,
                              UCAL_ACTUAL_MAXIMUM, &status);
}

static void set_day_of_year(icalrecur_iterator *impl, int doy)
{
    if (doy < 1) {
        doy += get_days_in_year(impl, 0);
    }

    ucal_set(impl->rscale, UCAL_DAY_OF_YEAR, (int32_t)doy);
}

static int get_start_of_week(icalrecur_iterator *impl)
{
    UErrorCode status = U_ZERO_ERROR;
    int doy, dow;

    doy = (int)ucal_get(impl->rscale, UCAL_DAY_OF_YEAR, &status);
    dow = (int)ucal_get(impl->rscale, UCAL_DAY_OF_WEEK, &status);
    dow -= (int)impl->rule->week_start;
    if (dow < 0) {
        dow += 7;
    }

    return (doy - dow);
}

static int get_day_of_week(icalrecur_iterator *impl)
{
    UErrorCode status = U_ZERO_ERROR;

    return (int)ucal_get(impl->rscale, UCAL_DAY_OF_WEEK, &status);
}

static int get_week_number(icalrecur_iterator *impl, struct icaltimetype tt)
{
    UErrorCode status = U_ZERO_ERROR;
    UDate last_millis;
    int month, weekno;

    /* Save existing rscale date */
    last_millis = ucal_getMillis(impl->rscale, &status);

    month = icalrecurrencetype_month_month(tt.month) - 1; /* UCal is 0-based */
    ucal_setDate(impl->rscale,
                 (int32_t)tt.year, (int32_t)month, (int32_t)tt.day, &status);
    if (icalrecurrencetype_month_is_leap(tt.month)) {
        ucal_set(impl->rscale, UCAL_IS_LEAP_MONTH, 1);
    }

    weekno = (int)ucal_get(impl->rscale, UCAL_WEEK_OF_YEAR, &status);

    /* Restore saved rscale date */
    ucal_setMillis(impl->rscale, last_millis, &status);

    return weekno;
}

static int get_days_in_month(icalrecur_iterator *impl, int month, int year)
{
    UErrorCode status = U_ZERO_ERROR;

    ucal_set(impl->rscale, UCAL_YEAR, (int32_t)year);

    if (!month) {
        month = impl->rstart.month;
    }
    __set_month(impl, month);

    return (int)ucal_getLimit(impl->rscale,
                              UCAL_DAY_OF_MONTH, UCAL_ACTUAL_MAXIMUM, &status);
}

static void prepare_rscale_adjusted(icalrecur_iterator *impl,
                                    int year, int month, int day, UErrorCode *status)
{
    ucal_set(impl->rscale, UCAL_YEAR, (int32_t)year);

    if (!month) {
        month = impl->rstart.month;
    }
    __set_month(impl, month);

    if (!day) {
        day = impl->rstart.day;
    } else if (day < 0) {
        day += 1 + (int)ucal_getLimit(impl->rscale, UCAL_DAY_OF_MONTH,
                                      UCAL_ACTUAL_MAXIMUM, status);
    }
    ucal_set(impl->rscale, UCAL_DAY_OF_MONTH, (int32_t)day);
}

static int get_day_of_year(icalrecur_iterator *impl,
                           int year, int month, int day)
{
    UErrorCode status = U_ZERO_ERROR;
    prepare_rscale_adjusted(impl, year, month, day, &status);
    return (int)ucal_get(impl->rscale, UCAL_DAY_OF_YEAR, &status);
}

static int get_day_of_week_adjusted(icalrecur_iterator *impl,
                                    int year, int month, int day)
{
    UErrorCode status = U_ZERO_ERROR;
    prepare_rscale_adjusted(impl, year, month, day, &status);
    return (int)ucal_get(impl->rscale, UCAL_DAY_OF_WEEK, &status);
}

static struct icaltimetype occurrence_as_icaltime(icalrecur_iterator *impl,
                                                  int normalize)
{
    struct icaltimetype tt = impl->dtstart;
    UErrorCode status = U_ZERO_ERROR;
    UCalendar *cal = impl->rscale;
    int is_leap_month = 0;

    if (normalize && (impl->rscale != impl->greg)) {
        /* Convert to Gregorian date */
        UDate millis = ucal_getMillis(impl->rscale, &status);

        ucal_setMillis(impl->greg, millis, &status);
        cal = impl->greg;
    } else {
        is_leap_month =
            (int)ucal_get(impl->rscale, UCAL_IS_LEAP_MONTH, &status);
    }

    tt.year = (int)ucal_get(cal, UCAL_YEAR, &status);
    tt.day = (int)ucal_get(cal, UCAL_DATE, &status);
    tt.month = 1 + /* UCal is 0-based */
               (int)ucal_get(cal, UCAL_MONTH, &status);
    if (is_leap_month) {
        tt.month |= LEAP_MONTH;
    }

    if (!tt.is_date) {
        tt.hour = (int)ucal_get(cal, UCAL_HOUR_OF_DAY, &status);
        tt.minute = (int)ucal_get(cal, UCAL_MINUTE, &status);
        tt.second = (int)ucal_get(cal, UCAL_SECOND, &status);
    }

    return tt;
}

static struct icaltimetype __icaltime_from_day_of_year(icalrecur_iterator *impl,
                                                       int day, int year, int *weekno)
{
    ucal_set(impl->rscale, UCAL_YEAR, (int32_t)year);
    if (day < 0) {
        day += get_days_in_year(impl, 0) + 1;
    }

    ucal_set(impl->rscale, UCAL_DAY_OF_YEAR, (int32_t)day);

    if (weekno) {
        UErrorCode status = U_ZERO_ERROR;

        *weekno = (int)ucal_get(impl->rscale, UCAL_WEEK_OF_YEAR, &status);
    }

    return occurrence_as_icaltime(impl, 0);
}

static void increment_year(icalrecur_iterator *impl, int inc)
{
    UErrorCode status = U_ZERO_ERROR;

    ucal_add(impl->rscale, UCAL_YEAR, (int32_t)inc, &status);
}

static void __increment_month(icalrecur_iterator *impl, int inc)
{
    UErrorCode status = U_ZERO_ERROR;

    ucal_add(impl->rscale, UCAL_MONTH, (int32_t)inc, &status);
}

static void increment_monthday(icalrecur_iterator *impl, int inc)
{
    UErrorCode status = U_ZERO_ERROR;

    ucal_add(impl->rscale, UCAL_DAY_OF_MONTH, (int32_t)inc, &status);
}

static void increment_hour(icalrecur_iterator *impl, int inc)
{
    UErrorCode status = U_ZERO_ERROR;

    ucal_add(impl->rscale, UCAL_HOUR_OF_DAY, (int32_t)inc, &status);
}

static void increment_minute(icalrecur_iterator *impl, int inc)
{
    UErrorCode status = U_ZERO_ERROR;

    ucal_add(impl->rscale, UCAL_MINUTE, (int32_t)inc, &status);
}

static void increment_second(icalrecur_iterator *impl, int inc)
{
    UErrorCode status = U_ZERO_ERROR;

    ucal_add(impl->rscale, UCAL_SECOND, (int32_t)inc, &status);
}

static bool validate_byrule(icalrecur_iterator *impl,
                            icalrecurrencetype_byrule byrule, UCalendarDateFields field,
                            short (*decode_val)(short *, bool),
                            bool decode_flags)
{
    if (has_by_data(impl, byrule)) {
        UErrorCode status = U_ZERO_ERROR;
        const icalrecurrence_by_data *by_ptr = &impl->bydata[byrule].by;
        short max =
            (short)ucal_getLimit(impl->rscale, field, UCAL_MAXIMUM, &status);
        short idx;

        for (idx = 0; idx < by_ptr->size; idx++) {
            short val = decode_val ? decode_val(&by_ptr->data[idx], decode_flags) : by_ptr->data[idx];

            if (abs(val) > max) {
                return false;
            }
        }
    }

    return true;
}

static short decode_month(short *month, bool is_hebrew)
{
    if (is_hebrew && *month > 5) { /* 5L == 0x1005 */
        /* Hebrew calendar:
           Translate RSCALE months to ICU (numbered 1-13, where 6 is leap).
           Hence, 5L maps to 6 and 6-12 map to 7-13. */
        *month = icalrecurrencetype_month_month(*month) + 1;
    }

    return icalrecurrencetype_month_month(*month) - 1; /* UCal is 0-based */
}

/* cppcheck-suppress constParameterCallback */
static short decode_day(short *day, bool flags) //NOLINT(readability-non-const-parameter)
{
    _unused(flags);

    return icalrecurrencetype_day_position(*day);
}

static bool initialize_rscale(icalrecur_iterator *impl)
{
    struct icalrecurrencetype *rule = impl->rule;
    struct icaltimetype dtstart = impl->dtstart;
    char locale[ULOC_KEYWORD_AND_VALUES_CAPACITY] = {0};
    UErrorCode status = U_ZERO_ERROR;
    UChar *tzid = (UChar *)UCAL_UNKNOWN_ZONE_ID;
    bool is_hebrew = false;

    /* Convert the UTF8 timezoneid of dstart to ICU UChar. */
    char *src = (char *)icaltimezone_get_location((icaltimezone *)dtstart.zone);
    if (!src) {
        const char *prefix = icaltimezone_tzid_prefix();
        src = (char *)icaltimezone_get_tzid((icaltimezone *)dtstart.zone);
        /* coverity[use_after_free] */
        if (src && !strncmp(src, prefix, strlen(prefix))) {
            /* Skip past our prefix */
            src += strlen(prefix);
        }
    }
    if (src) {
        size_t len = (strlen(src) + 1) * U_SIZEOF_UCHAR;
        tzid = icalmemory_tmp_buffer(len);
        tzid = u_strFromUTF8Lenient(tzid, (int32_t)len, NULL, src, -1, &status);
        if (U_FAILURE(status)) {
            icalerror_set_errno(ICAL_INTERNAL_ERROR);
            return false;
        }
    }

    /* Create locale for Gregorian calendar */
    (void)uloc_setKeywordValue("calendar", "gregorian",
                               locale, sizeof(locale), &status);

    /* Create Gregorian calendar and set to DTSTART */
    impl->greg = ucal_open(tzid, -1, locale, UCAL_DEFAULT, &status);
    if (impl->greg) {
        ucal_setDateTime(impl->greg,
                         (int32_t)dtstart.year,
                         (int32_t)(dtstart.month - 1), /* UCal is 0-based */
                         (int32_t)dtstart.day,
                         (int32_t)dtstart.hour,
                         (int32_t)dtstart.minute,
                         (int32_t)dtstart.second, &status);
    }
    if (!impl->greg || U_FAILURE(status)) {
        icalerror_set_errno(ICAL_INTERNAL_ERROR);
        return false;
    }

    if (!rule->rscale) {
        /* Use Gregorian as RSCALE */
        impl->rscale = impl->greg;
    } else {
        UEnumeration *en;
        const char *cal;
        char *r;

        /* Lowercase the specified calendar */
        for (r = rule->rscale; *r; r++) {
            *r = tolower((int)*r);
        }

        /* Check if specified calendar is supported */
        en = ucal_getKeywordValuesForLocale("calendar", "", false, &status);
        while ((cal = uenum_next(en, NULL, &status))) {
            if (!strcmp(cal, rule->rscale)) {
                is_hebrew = !strcmp(rule->rscale, "hebrew");
                break;
            }
        }
        uenum_close(en);
        if (!cal) {
            icalerror_set_errno(ICAL_UNIMPLEMENTED_ERROR);
            return false;
        }

        /* Create locale for RSCALE calendar */
        (void)uloc_setKeywordValue("calendar", rule->rscale,
                                   locale, sizeof(locale), &status);

        /* Create RSCALE calendar and set to DTSTART */
        impl->rscale = ucal_open(tzid, -1, locale, UCAL_DEFAULT, &status);
        if (impl->rscale) {
            UDate millis = ucal_getMillis(impl->greg, &status);

            ucal_setMillis(impl->rscale, millis, &status);
        }
        if (!impl->rscale || U_FAILURE(status)) {
            icalerror_set_errno(ICAL_INTERNAL_ERROR);
            return false;
        }
    }

    /* Validate BY_* array values whose legal maximums differ based on RSCALE */
    if (!validate_byrule(impl, ICAL_BY_MONTH, UCAL_MONTH,
                         &decode_month, is_hebrew) ||
        !validate_byrule(impl, ICAL_BY_DAY, UCAL_WEEK_OF_YEAR, &decode_day, 0) ||
        !validate_byrule(impl, ICAL_BY_MONTH_DAY, UCAL_DAY_OF_MONTH, NULL, 0) ||
        !validate_byrule(impl, ICAL_BY_YEAR_DAY, UCAL_DAY_OF_YEAR, NULL, 0) ||
        !validate_byrule(impl, ICAL_BY_WEEK_NO, UCAL_WEEK_OF_YEAR, NULL, 0) ||
        !validate_byrule(impl, ICAL_BY_SET_POS, UCAL_DAY_OF_YEAR, NULL, 0)) {
        icalerror_set_errno(ICAL_MALFORMEDDATA_ERROR);
        return false;
    }

    /* Set iCalendar defaults */
    ucal_setAttribute(impl->rscale, UCAL_MINIMAL_DAYS_IN_FIRST_WEEK, 4);
    ucal_setAttribute(impl->rscale, UCAL_FIRST_DAY_OF_WEEK, (int32_t)rule->week_start);

    /* Get rstart (DTSTART in RSCALE) */
    impl->rstart = occurrence_as_icaltime(impl, 0);

    return true;
}

static void set_start(icalrecur_iterator *impl, icaltimetype date)
{
    UErrorCode status = U_ZERO_ERROR;

    impl->last.is_date = impl->rstart.is_date;
    impl->last.zone = impl->rstart.zone;

    if (impl->rstart.is_date) {
        ucal_setDate(impl->greg,
                     (int32_t)date.year,
                     (int32_t)(date.month - 1), /* UCal is 0-based */
                     (int32_t)date.day, &status);
    } else {
        int hour, minute, second;

        __get_start_time(impl, date, &hour, &minute, &second);

        ucal_setDateTime(impl->greg,
                         (int32_t)date.year,
                         (int32_t)(date.month - 1), /* UCal is 0-based */
                         (int32_t)date.day,
                         (int32_t)hour,
                         (int32_t)minute,
                         (int32_t)second,
                         &status);
    }

    if (impl->rscale != impl->greg) {
        UDate millis = ucal_getMillis(impl->greg, &status);
        ucal_setMillis(impl->rscale, millis, &status);
    }
}

static void set_datetime(icalrecur_iterator *impl, icaltimetype date)
{
    UErrorCode status = U_ZERO_ERROR;

    impl->last.is_date = impl->rstart.is_date;
    impl->last.zone = impl->rstart.zone;

    if (impl->rstart.is_date) {
        ucal_setDate(impl->greg,
                     (int32_t)date.year,
                     (int32_t)(date.month - 1), /* UCal is 0-based */
                     (int32_t)date.day, &status);
    } else {
        ucal_setDateTime(impl->greg,
                         (int32_t)date.year,
                         (int32_t)(date.month - 1), /* UCal is 0-based */
                         (int32_t)date.day,
                         (int32_t)date.hour,
                         (int32_t)date.minute,
                         (int32_t)date.second,
                         &status);
    }

    if (impl->rscale != impl->greg) {
        UDate millis = ucal_getMillis(impl->greg, &status);
        ucal_setMillis(impl->rscale, millis, &status);
    }
}

static int month_diff(icalrecur_iterator *impl, icaltimetype a, icaltimetype b)
{
    int diff;

    if (impl->rscale == impl->greg) {
        /* Use simple Gregorian math */
        diff = __greg_month_diff(a, b);
    } else if (a.year == b.year) {
        diff = b.month - a.month;
    } else {
        /* Count months in each year to account for leap months */
        UErrorCode status = U_ZERO_ERROR;
        UDate millis;
        int year = a.year;

        /* Save current date */
        millis = ucal_getMillis(impl->rscale, &status);

        set_day_of_year(impl, 1);
        diff = get_months_in_year(impl, year) - a.month;
        while (++year < b.year) {
            diff += get_months_in_year(impl, year);
        }
        diff += b.month;

        /* Restore date */
        ucal_setMillis(impl->rscale, millis, &status);
    }

    return diff;
}

static int day_diff(icalrecur_iterator *impl, icaltimetype a, icaltimetype b)
{
    UErrorCode status = U_ZERO_ERROR;
    UDate millis;
    int diff;

    /* Save current date */
    millis = ucal_getMillis(impl->rscale, &status);

    set_day_of_year(impl, 1);

    diff = __day_diff(impl, a, b);

    /* Restore date */
    ucal_setMillis(impl->rscale, millis, &status);

    return diff;
}

static void reset_period_start(icalrecur_iterator *impl)
{
    struct icaltimetype start = impl->period_start;

    (void)get_day_of_year(impl, start.year, start.month, start.day);
}

#else /* !HAVE_LIBICU */

/*
 * Callbacks for recurrence rules without RSCALE (Gregorian only)
 */

icalarray *icalrecurrencetype_rscale_supported_calendars(void)
{
    icalarray *calendars = icalarray_new(sizeof(const char **), 1);
    const char *cal = "GREGORIAN";

    icalarray_append(calendars, &cal);

    return calendars;
}

static void set_second(icalrecur_iterator *impl, int second)
{
    impl->last.second = second;
}

static void set_minute(icalrecur_iterator *impl, int minute)
{
    impl->last.minute = minute;
}

static void set_hour(icalrecur_iterator *impl, int hour)
{
    impl->last.hour = hour;
}

static int set_month(icalrecur_iterator *impl, int month)
{
    return (impl->last.month = month);
}

#define get_months_in_year(impl, year) (12)

static int get_days_in_year(icalrecur_iterator *impl, int year)
{
    _unused(impl);

    return icaltime_days_in_year(year);
}

static void set_day_of_year(icalrecur_iterator *impl, int doy)
{
    struct icaltimetype next;

    if (doy < 1) {
        doy += get_days_in_year(impl, impl->last.year);
    }

    next = icaltime_from_day_of_year(doy, impl->last.year);

    impl->last.day = next.day;
    impl->last.month = next.month;
    impl->last.year = next.year;
}

static int get_start_of_week(const icalrecur_iterator *impl)
{
    return icaltime_start_doy_week(impl->last, (int)impl->rule->week_start);
}

static int get_day_of_week(const icalrecur_iterator *impl)
{
    return icaltime_day_of_week(impl->last);
}

static int get_week_number(icalrecur_iterator *impl, struct icaltimetype tt)
{
    int dow, week;

    _unused(impl);

    /* Normalize day of week so that week_start day is 1 */
    dow = icaltime_day_of_week(tt) - (int)(impl->rule->week_start - 1);
    if (dow <= 0) {
        dow += 7;
    }

    week = (icaltime_day_of_year(tt) - dow + 10) / 7;
    if (week < 1) {
        /* Last week of preceding year */
        week = weeks_in_year(tt.year - 1);
    } else if (week > weeks_in_year(tt.year)) {
        /* First week of following year */
        week = 1;
    }

    return week;
}

static int get_days_in_month(icalrecur_iterator *impl, int month, int year)
{
    _unused(impl);

    return icaltime_days_in_month(month, year);
}

static struct icaltimetype get_dtstart_adjusted(icalrecur_iterator *impl,
                                                int year, int month, int day)
{
    struct icaltimetype t = impl->dtstart;

    t.is_date = 1;
    t.year = year;

    if (!month) {
        month = impl->dtstart.month;
    }
    t.month = month;

    if (!day) {
        day = impl->dtstart.day;
    } else if (day < 0) {
        day += icaltime_days_in_month(month, year) + 1;
    }
    t.day = day;

    return t;
}

static int get_day_of_year(icalrecur_iterator *impl,
                           int year, int month, int day)
{
    return icaltime_day_of_year(get_dtstart_adjusted(impl, year, month, day));
}

static int get_day_of_week_adjusted(icalrecur_iterator *impl,
                                    int year, int month, int day)
{
    return icaltime_day_of_week(get_dtstart_adjusted(impl, year, month, day));
}

static struct icaltimetype occurrence_as_icaltime(icalrecur_iterator *impl,
                                                  int normalize)
{
    return (normalize ? icaltime_normalize(impl->last) : impl->last);
}

static struct icaltimetype __icaltime_from_day_of_year(icalrecur_iterator *impl,
                                                       int day, int year, int *weekno)
{
    struct icaltimetype tt;

    if (day < 0) {
        day += get_days_in_year(impl, year) + 1;
    }

    tt = icaltime_from_day_of_year(day, year);

    if (weekno) {
        *weekno = get_week_number(impl, tt);
    }
    return tt;
}

static void increment_year(icalrecur_iterator *impl, int inc)
{
    impl->last.year += inc;
}

static void __increment_month(icalrecur_iterator *impl, int inc)
{
    int years;

    impl->last.month += inc;

    /* Months are offset by one */
    impl->last.month--;

    years = impl->last.month / 12;

    impl->last.month = impl->last.month % 12;

    if (impl->last.month < 0) {
        impl->last.month = impl->last.month + 12;
        years--;
    }

    impl->last.month++;

    if (years != 0) {
        increment_year(impl, years);
    }
}

static void increment_monthday(icalrecur_iterator *impl, int inc)
{
    icaltime_adjust(&impl->last, inc, 0, 0, 0);
}

static void increment_hour(icalrecur_iterator *impl, int inc)
{
    icaltime_adjust(&impl->last, 0, inc, 0, 0);
}

static void increment_minute(icalrecur_iterator *impl, int inc)
{
    icaltime_adjust(&impl->last, 0, 0, inc, 0);
}

static void increment_second(icalrecur_iterator *impl, int inc)
{
    icaltime_adjust(&impl->last, 0, 0, 0, inc);
}

static bool initialize_rscale(icalrecur_iterator *impl)
{
    if (impl->rule->rscale && strcasecmp(impl->rule->rscale, "GREGORIAN")) {
        icalerror_set_errno(ICAL_UNIMPLEMENTED_ERROR);
        return false;
    }

    impl->rstart = impl->dtstart;

    return true;
}

static void set_start(icalrecur_iterator *impl, icaltimetype date)
{
    impl->last.year = date.year;
    impl->last.month = date.month;
    impl->last.day = date.day;
    impl->last.is_date = impl->dtstart.is_date;
    impl->last.zone = impl->dtstart.zone;

    if (!impl->dtstart.is_date) {
        __get_start_time(impl, date, &impl->last.hour,
                         &impl->last.minute, &impl->last.second);
    }
}

static void set_datetime(icalrecur_iterator *impl, icaltimetype date)
{
    impl->last = date;
}

static int month_diff(icalrecur_iterator *impl, icaltimetype a, icaltimetype b)
{
    _unused(impl);

    return __greg_month_diff(a, b);
}

static int day_diff(icalrecur_iterator *impl, icaltimetype a, icaltimetype b)
{
    return __day_diff(impl, a, b);
}

static void reset_period_start(icalrecur_iterator *impl)
{
    /* We only want to set the date, not the time */
    impl->last.year = impl->period_start.year;
    impl->last.month = impl->period_start.month;
    impl->last.day = impl->period_start.day;
}

#endif /* HAVE_LIBICU */

static int get_second(icalrecur_iterator *impl)
{
    return occurrence_as_icaltime(impl, 1).second;
}

static int get_minute(icalrecur_iterator *impl)
{
    return occurrence_as_icaltime(impl, 1).minute;
}

static int get_hour(icalrecur_iterator *impl)
{
    return occurrence_as_icaltime(impl, 1).hour;
}

static bool __iterator_set_start(icalrecur_iterator *impl, icaltimetype start);
static void increment_month(icalrecur_iterator *impl, int inc);
static void expand_month_days(icalrecur_iterator *impl, int year, int month);
static void expand_year_days(icalrecur_iterator *impl, int year);
static int next_yearday(icalrecur_iterator *impl,
                        void (*next_period)(icalrecur_iterator *, int));
static int prev_yearday(icalrecur_iterator *impl,
                        void (*next_period)(icalrecur_iterator *, int));

static void adjust_to_byday(icalrecur_iterator *impl)
{
    /* If there is ICAL_BY_DAY data, then we need to move the initial
       time to the start of the ICAL_BY_DAY data. That is if the
       start time is on a Wednesday, and the rule has
       BYDAY=MO,WE,FR, move the initial time back to
       monday. Otherwise, jumping to the next week ( jumping 7
       days ahead ) will skip over some occurrences in the
       second week. */

    /* This depends on impl->bydata[ICAL_BY_DAY].by.data being correctly sorted by
     * day. This should probably be abstracted to make such assumption
     * more explicit. */
    short this_dow = (short)get_day_of_week(impl);
    short dow = (short)(impl->bydata[ICAL_BY_DAY].by.data[0] - this_dow);

    /* Normalize day of week around week start */
    if (dow != 0 && this_dow < (short)impl->rule->week_start) {
        dow -= 7;
    }

    if ((this_dow < impl->bydata[ICAL_BY_DAY].by.data[0] && dow >= 0) || dow < 0) {
        /* initial time is after first day of ICAL_BY_DAY data */
        increment_monthday(impl, dow);
    }
}

icalrecur_iterator *icalrecur_iterator_new(struct icalrecurrencetype *rule,
                                           struct icaltimetype dtstart)
{
    if (rule == NULL) {
        icalerror_set_errno(ICAL_USAGE_ERROR);
        return 0;
    }

    icalrecur_iterator *impl;
    icalrecurrencetype_frequency freq = rule->freq;
    icalrecurrencetype_byrule byrule;

    icalerror_clear_errno();

    if (freq == ICAL_NO_RECURRENCE) {
        icalerror_set_errno(ICAL_MALFORMEDDATA_ERROR);
        return 0;
    }

#define IN_RANGE(val, min, max) ((val) >= (min) && (val) <= (max))
    /* Make sure that DTSTART is a sane value */
    if (!icaltime_is_valid_time(dtstart) ||
        !IN_RANGE(dtstart.year, 0, MAX_TIME_T_YEAR) ||
        !IN_RANGE(dtstart.month, 1, 12) ||
        !IN_RANGE(dtstart.day, 1,
                  icaltime_days_in_month(dtstart.month, dtstart.year)) ||
        (!dtstart.is_date && (!IN_RANGE(dtstart.hour, 0, 23) ||
                              !IN_RANGE(dtstart.minute, 0, 59) ||
                              !IN_RANGE(dtstart.second, 0, 59)))) {
        icalerror_set_errno(ICAL_MALFORMEDDATA_ERROR);
        return 0;
    }

    if (!(impl = (icalrecur_iterator *)icalmemory_new_buffer(sizeof(icalrecur_iterator)))) {
        icalerror_set_errno(ICAL_NEWFAILED_ERROR);
        return 0;
    }

    memset(impl, 0, sizeof(icalrecur_iterator));

    impl->dtstart = dtstart;

#if defined(HAVE_LIBICU)
    if (rule->rscale) {
        // The referenced rule should be treated as immutable, but in case of rscale we need
        // to modify it (change rscale to lower, shift months in decode_month()), so we
        // clone the whole rule and leave the original one untouched.
        rule = icalrecurrencetype_clone(rule);
        if (!rule) {
            icalerror_set_errno(ICAL_NEWFAILED_ERROR);
            icalmemory_free_buffer(impl);
            return 0;
        }
    } else
#endif
    {
        // Without rscale we don't need to modify the rule state. We need to populate some by
        // values if they aren't set, but we have dedicated storage for that within the
        // iterator (i.e. icalrecurrence_iterator_by_data.buffer_value). So we simply ref
        // the rule but don't clone it.
        icalrecurrencetype_ref(rule);
    }

    impl->rule = rule;

    impl->iend = icaltime_null_time();

    for (byrule = 0; byrule < ICAL_BY_NUM_PARTS; ++byrule) {
        impl->bydata[byrule].by = impl->rule->by[byrule];

        /* Note which by rules had data in them when the iterator was
        created. We can't use the actual by_x arrays, because the
        empty ones will be given default values later in this
        routine. The orig_data array will be used later in has_by_data */

        impl->bydata[byrule].orig_data =
            (short)(impl->rule->by[byrule].size > 0);

        /* Check if the recurrence rule is legal */
        if (expand_map[freq].map[byrule] == ILLEGAL &&
            has_by_data(impl, byrule)) {
            ical_invalid_rrule_handling rruleHandlingSetting =
                ical_get_invalid_rrule_handling_setting();
            if (rruleHandlingSetting == ICAL_RRULE_IGNORE_INVALID) {
                impl->bydata[byrule].orig_data = 0;
            } else {
                icalerror_set_errno(ICAL_MALFORMEDDATA_ERROR);
                icalmemory_free_buffer(impl);
                return 0;
            }
        }
    }

    if (initialize_rscale(impl) == 0) {
        icalrecur_iterator_free(impl);
        return 0;
    }

    /* Set up defaults for BY_* arrays */
    setup_defaults(impl, ICAL_BY_SECOND, impl->rstart.second);

    setup_defaults(impl, ICAL_BY_MINUTE, impl->rstart.minute);

    setup_defaults(impl, ICAL_BY_HOUR, impl->rstart.hour);

    setup_defaults(impl, ICAL_BY_MONTH_DAY, impl->rstart.day);

    setup_defaults(impl, ICAL_BY_MONTH, impl->rstart.month);

    if (has_by_data(impl, ICAL_BY_SET_POS)) {
        impl->sp_pmax = 0;
        while (impl->sp_pmax < impl->bydata[ICAL_BY_SET_POS].by.size &&
               impl->bydata[ICAL_BY_SET_POS].by.data[impl->sp_pmax] > 0) {
            impl->sp_pmax++;
        }
        impl->sp_pmax--;
    }

    if (!__iterator_set_start(impl, dtstart)) {
        icalrecur_iterator_free(impl);
        return 0;
    }

    return impl;
}

void icalrecur_iterator_free(icalrecur_iterator *impl)
{
    icalerror_check_arg_rv((impl != 0), "impl");

#if defined(HAVE_LIBICU)
    if (impl->greg) {
        if (impl->rscale && (impl->rscale != impl->greg)) {
            ucal_close(impl->rscale);
        }

        ucal_close(impl->greg);
    }
#endif

    icalrecurrencetype_unref(impl->rule);
    icalmemory_free_buffer(impl);
}

static int __day_diff(icalrecur_iterator *impl, icaltimetype a, icaltimetype b)
{
    int diff;

    if (a.year == b.year) {
        diff = get_day_of_year(impl, b.year, b.month, b.day) -
               get_day_of_year(impl, a.year, a.month, a.day);
    } else {
        /* Swap a and b if a is greater than b */
        int flipped = 0;
        int year;

        if (a.year > b.year) {
            icaltimetype temp = a;

            a = b;
            b = temp;
            flipped = 1;
        }

        /* Count days in each year to account for leap days/months */
        year = a.year;

        diff = get_days_in_year(impl, year) -
               get_day_of_year(impl, a.year, a.month, a.day);
        while (++year < b.year) {
            diff += get_days_in_year(impl, year);
        }
        diff += get_day_of_year(impl, b.year, b.month, b.day);

        if (flipped) {
            /* The difference is negative because a was greater than b */
            diff = -diff;
        }
    }

    return diff;
}

static void increment_month(icalrecur_iterator *impl, int inc)
{
    __increment_month(impl, inc);

    if (has_by_data(impl, ICAL_BY_MONTH)) {
        struct icaltimetype this = occurrence_as_icaltime(impl, 0);

        while (this.year < MAX_TIME_T_YEAR) {
            icalrecurrence_iterator_by_data *bydata = &impl->bydata[ICAL_BY_MONTH];
            for (bydata->index = 0;
                 bydata->index < bydata->by.size; bydata->index++) {
                if (this.month == bydata->by.data[bydata->index]) {
                    return;
                }
            }

            __increment_month(impl, inc);
            this = occurrence_as_icaltime(impl, 0);
        }
    }
}

static int next_unit(icalrecur_iterator *impl,
                     int by_unit, icalrecurrencetype_frequency frequency,
                     int (*next_sub_unit)(icalrecur_iterator *),
                     void (*set_unit)(icalrecur_iterator *, int),
                     int (*get_unit)(icalrecur_iterator *),
                     int period_len,
                     void (*increment_unit)(icalrecur_iterator *, int))
{
    int has_by_unit = (by_unit > ICAL_BYRULE_NO_CONTRACTION) &&
                      (impl->bydata[by_unit].by.size > 0);
    int this_frequency = (impl->rule->freq == frequency);

    int end_of_data = 0;

    icalassert(has_by_unit || this_frequency);

    if (next_sub_unit && next_sub_unit(impl) == 0) {
        return 0;
    }

    const size_t max_recurrence_time_count = icallimit_get(ICAL_LIMIT_RECURRENCE_TIME_STANDING_STILL);
    if (has_by_unit) {
        /* Frequency must be hours, minutes or seconds */
        icalrecurrence_iterator_by_data *bydata = &impl->bydata[by_unit];
        if (this_frequency) {
            bydata->index++;
            /* Take the frequency into account and treat the byrule data as limiting */
            size_t stalledCnt = 0;
            while ((impl->last.year < MAX_TIME_T_YEAR) && (stalledCnt++ < max_recurrence_time_count)) {
                int last_unit = get_unit(impl);
                /* Find a BY* value that works with the interval length */
                while (bydata->index < bydata->by.size) {
                    int cur_by = bydata->by.data[bydata->index];
                    if ((cur_by >= last_unit) &&
                        ((cur_by - last_unit) % impl->rule->interval) == 0) {
                        set_unit(impl, cur_by);
                        return 1;
                    }
                    bydata->index++;
                }
                /* If none found, increment to next period (i.e., increment super unit,
                 * but take into account interval length). */
                bydata->index = 0;
                int multiplier = 1;
                if (last_unit + impl->rule->interval < period_len) {
                    int diff = period_len - last_unit;
                    multiplier = (diff / impl->rule->interval + (diff % impl->rule->interval > 0));
                }
                increment_unit(impl, multiplier * impl->rule->interval);
            }
        } else {
            bydata->index++;

            if (bydata->by.size <= bydata->index) {
                bydata->index = 0;

                end_of_data = 1;
            }

            if (bydata->index < bydata->by.size) {
                set_unit(impl, bydata->by.data[bydata->index]);
            } else {
                icalerror_set_errno(ICAL_INTERNAL_ERROR);
            }
        }
    } else {
        /* Compute the next value from the last time and the freq interval */
        increment_unit(impl, impl->rule->interval);
        end_of_data = 1;
    }

    return end_of_data;
}

static int next_second(icalrecur_iterator *impl)
{
    return next_unit(impl, ICAL_BY_SECOND, ICAL_SECONDLY_RECURRENCE, NULL,
                     &set_second, &get_second, 60, &increment_second);
}

static int next_minute(icalrecur_iterator *impl)
{
    return next_unit(impl, ICAL_BY_MINUTE, ICAL_MINUTELY_RECURRENCE, &next_second,
                     &set_minute, &get_minute, 60, &increment_minute);
}

static int next_hour(icalrecur_iterator *impl)
{
    return next_unit(impl, ICAL_BY_HOUR, ICAL_HOURLY_RECURRENCE, &next_minute,
                     &set_hour, &get_hour, 24, &increment_hour);
}

static int next_day(icalrecur_iterator *impl)
{
    return next_unit(impl, ICAL_BYRULE_NO_CONTRACTION, ICAL_DAILY_RECURRENCE, &next_hour,
                     NULL, NULL, 0, &increment_monthday);
}

static int prev_unit(icalrecur_iterator *impl,
                     int by_unit, icalrecurrencetype_frequency frequency,
                     int (*prev_sub_unit)(icalrecur_iterator *),
                     void (*set_unit)(icalrecur_iterator *, int),
                     int (*get_unit)(icalrecur_iterator *),
                     void (*increment_unit)(icalrecur_iterator *, int))
{
    int has_by_unit = (by_unit > ICAL_BYRULE_NO_CONTRACTION) &&
                      (impl->bydata[by_unit].by.size > 0);
    int this_frequency = (impl->rule->freq == frequency);

    int end_of_data = 0;

    icalassert(has_by_unit || this_frequency);

    if (prev_sub_unit && prev_sub_unit(impl) == 0) {
        return 0;
    }

    if (has_by_unit) {
        icalrecurrence_iterator_by_data *bydata = &impl->bydata[by_unit];
        if (this_frequency) {
            bydata->index--;

            while (impl->last.year > 0) {
                int last_unit = get_unit(impl);
                while (bydata->index >= 0) {
                    int cur_by = bydata->by.data[bydata->index];
                    if ((cur_by <= last_unit) && (impl->rule->interval > 0) &&
                        ((last_unit - cur_by) % impl->rule->interval) == 0) {
                        set_unit(impl, cur_by);
                        return 1;
                    }
                    bydata->index--;
                }
                bydata->index = bydata->by.size - 1;
                int multiplier = 1;
                if (last_unit - impl->rule->interval > 0) {
                    multiplier = (last_unit / impl->rule->interval + (last_unit % impl->rule->interval > 0));
                }
                increment_unit(impl, -multiplier * impl->rule->interval);
            }
        } else {
            bydata->index--;

            if (bydata->index < 0) {
                bydata->index =
                    bydata->by.size - 1;

                end_of_data = 1;
            }

            set_unit(impl, bydata->by.data[bydata->index]);
        }

    } else {
        /* Compute the next value from the last time and the freq interval */
        increment_unit(impl, -impl->rule->interval);
        end_of_data = 1;
    }

    return end_of_data;
}

static int prev_second(icalrecur_iterator *impl)
{
    return prev_unit(impl, ICAL_BY_SECOND, ICAL_SECONDLY_RECURRENCE, NULL,
                     &set_second, &get_second, &increment_second);
}

static int prev_minute(icalrecur_iterator *impl)
{
    return prev_unit(impl, ICAL_BY_MINUTE, ICAL_MINUTELY_RECURRENCE, &prev_second,
                     &set_minute, &get_minute, &increment_minute);
}

static int prev_hour(icalrecur_iterator *impl)
{
    return prev_unit(impl, ICAL_BY_HOUR, ICAL_HOURLY_RECURRENCE, &prev_minute,
                     &set_hour, &get_hour, &increment_hour);
}

static int prev_day(icalrecur_iterator *impl)
{
    return prev_unit(impl, ICAL_BYRULE_NO_CONTRACTION, ICAL_DAILY_RECURRENCE, &prev_hour,
                     NULL, NULL, &increment_monthday);
}

static void expand_bymonth_days(icalrecur_iterator *impl, int year, int month)
{
    int i;
    int days_in_month = get_days_in_month(impl, month, year);

    for (i = 0; i < impl->bydata[ICAL_BY_MONTH_DAY].by.size; i++) {
        short doy = ICAL_BY_YEARDAY_SIZE, mday = impl->bydata[ICAL_BY_MONTH_DAY].by.data[i];
        int this_month = month;

        if (abs(mday) > days_in_month) {
            int days_in_year = get_days_in_year(impl, year);

            switch (impl->rule->skip) {
            default:
                /* Should never get here! */

            case ICAL_SKIP_OMIT:
                continue;

            case ICAL_SKIP_FORWARD:
                if (mday > 0) {
                    this_month++; /* Next month */
                }

                if (this_month > get_months_in_year(impl, year)) {
                    doy = days_in_year + 1; /* First day of next year */
                } else {
                    mday = 1; /* First day of month */
                }
                break;

            case ICAL_SKIP_BACKWARD:
                if (mday < 0) {
                    this_month--; /* Prev month */
                }

                if (this_month == 0) {
                    doy = 0; /* Last day of prev year */
                } else {
                    mday = -1; /* Last day of month */
                }
                break;
            }
        }

        if (doy == ICAL_BY_YEARDAY_SIZE) {
            doy = get_day_of_year(impl, year, this_month, mday);
        }

        daysmask_setbit(impl->days, doy, 1);
        if (doy < impl->days_index) {
            impl->days_index = doy;
        }
    }
}

static void expand_by_day(icalrecur_iterator *impl, int year,
                          int doy_offset, int last_day,
                          int first_dow, int last_dow,
                          int is_limiting)
{
    /* Try to calculate each of the occurrences. */
    unsigned long bydays[LONGS_PER_BITS(ICAL_YEARDAYS_MASK_SIZE)];
    int i;

    memcpy(bydays, impl->days, sizeof(bydays));

    daysmask_set_range(impl->days, doy_offset + 1, doy_offset + last_day + 1, 0);

    for (i = 0; i < impl->bydata[ICAL_BY_DAY].by.size; i++) {
        /* This is 1 (Sun) to 7 (Sat). */
        int dow = (int)icalrecurrencetype_day_day_of_week(impl->bydata[ICAL_BY_DAY].by.data[i]);
        int pos = icalrecurrencetype_day_position(impl->bydata[ICAL_BY_DAY].by.data[i]);
        int first_matching_day, last_matching_day;
        int day, this_weekno;

        /* Calculate the first day in the period
           with the given weekday, and the last day. */
        first_matching_day = ((dow + 7 - first_dow) % 7) + 1;
        last_matching_day = last_day - ((last_dow + 7 - dow) % 7);

        if (pos == 0) {
            /* First instance of the weekday within the period.
               (Remaining instances added by loop below. */
            day = first_matching_day;

        } else if (pos > 0) {
            /* nth instance of the weekday within the period. */
            day = first_matching_day + (pos - 1) * 7;

            if (day > last_matching_day) {
                continue;
            }

        } else { /* pos < 0 */
            /* -nth instance of the weekday within the period. */
            day = last_matching_day + (pos + 1) * 7;

            if (day < first_matching_day) {
                continue;
            }
        }

        if (doy_offset < 0) {
            this_weekno = 1;
        } else {
            (void)__icaltime_from_day_of_year(impl, day + doy_offset, year,
                                              &this_weekno);
        }

        /* Add instance(s) of the weekday within the period */
        do {
            int valid = 0;

            if (has_by_data(impl, ICAL_BY_WEEK_NO)) {
                /* Make sure our day falls in one of the BYWEEKNO */
                int nweeks = weeks_in_year(year);
                int j;

                for (j = 0; j < impl->bydata[ICAL_BY_WEEK_NO].by.size; j++) {
                    int weekno = impl->bydata[ICAL_BY_WEEK_NO].by.data[j];

                    if (weekno < 0) {
                        weekno += nweeks + 1;
                    }

                    if (weekno == this_weekno) {
                        valid = 1;
                        break;
                    }
                }
            } else {
                valid = 1;
            }

            if (valid) {
                int new_val = is_limiting
                                  /* "Filter" the year days bitmask with the bydays bitmask */
                                  ? (int)daysmask_getbit(bydays, day + doy_offset)
                                  /* Add each BYDAY to the year days bitmask */
                                  : 1;

                if (!daysmask_setbit(impl->days, day + doy_offset, new_val) && new_val) {
                    if (day + doy_offset < impl->days_index) {
                        impl->days_index = day + doy_offset;
                    }
                }
            }

        } while (!pos && ((day += 7) <= last_day) && ++this_weekno);
    }
}

static void expand_month_days(icalrecur_iterator *impl, int year, int month)
{
    int doy_offset, days_in_month, first_dow;

    daysmask_clearall(impl->days);

    /* We may end up skipping fwd/bwd a month during expansion.
       Mark our current start date so next_month() can increment from here */
    impl->period_start = occurrence_as_icaltime(impl, 0);

    doy_offset = get_day_of_year(impl, year, month, 1) - 1;
    first_dow = get_day_of_week_adjusted(impl, year, month, 1);
    days_in_month = get_days_in_month(impl, month, year);

    /* Add each BYMONTHDAY to the year days bitmask */
    expand_bymonth_days(impl, year, month);

    if (has_by_data(impl, ICAL_BY_DAY)) {
        /* Apply each BYDAY to the year days bitmask */
        int last_dow;

        impl->days_index = ICAL_YEARDAYS_MASK_SIZE;

        last_dow = get_day_of_week_adjusted(impl, year, month, days_in_month);

        expand_by_day(impl, year, doy_offset, days_in_month,
                      first_dow, last_dow,
                      has_by_data(impl, ICAL_BY_MONTH_DAY));
    }
}

static void __next_month(icalrecur_iterator *impl, int inc)
{
    struct icaltimetype this;

    /* Increment to and expand the next month */
    increment_month(impl, inc);
    this = occurrence_as_icaltime(impl, 0);
    expand_month_days(impl, this.year, this.month);
}

static int next_month(icalrecur_iterator *impl)
{
    return next_yearday(impl, &__next_month);
}

static int prev_month(icalrecur_iterator *impl)
{
    return prev_yearday(impl, &__next_month);
}

static int next_weekday_by_week(icalrecur_iterator *impl)
{
    int end_of_data = 0;

    if (next_hour(impl) == 0) {
        return 0;
    }

    if (!has_by_data(impl, ICAL_BY_DAY)) {
        return 1;
    }

    /* If we get here, we need to step to the next day */

    for (;;) {
        impl->bydata[ICAL_BY_DAY].index++; /* Look at next elem in BYDAY array */

        /* Are we at the end of the BYDAY array? */
        if (impl->bydata[ICAL_BY_DAY].index >= impl->bydata[ICAL_BY_DAY].by.size) {
            impl->bydata[ICAL_BY_DAY].index = 0; /* Reset to 0 */
            end_of_data = 1;                     /* Signal that we're at the end */
        }

        /* Add the day of week offset to the start of this week, and use
           that to get the next day */
        /* ignore position of dow ("4FR"), only use dow ("FR") */
        int dow = (int)icalrecurrencetype_day_day_of_week(
            impl->bydata[ICAL_BY_DAY].by.data[impl->bydata[ICAL_BY_DAY].index]);
        dow -= (int)impl->rule->week_start; /* Set Sunday to be 0 */
        if (dow < 0) {
            dow += 7;
        }

        int start_of_week = get_start_of_week(impl);

        if (dow + start_of_week < 1) {
            /* The selected date is in the previous year. */
            if (!end_of_data) {
                continue;
            }

            increment_year(impl, -1);
        }

        set_day_of_year(impl, start_of_week + dow);

        return end_of_data;
    }
}

static bool next_week(icalrecur_iterator *impl)
{
    /* Increment to the next week day,
       if there is data at a level less than a week */
    if (next_weekday_by_week(impl) == 0) {
        return 0; /* Have not reached end of week yet */
    }

    /* If we get here, we have incremented through the entire week, and
       can increment to the next week */

    /* Jump to the next week */
    increment_monthday(impl, 7 * impl->rule->interval);

    return 1;
}

static int prev_weekday_by_week(icalrecur_iterator *impl)
{
    int end_of_data = 0;
    int start_of_week, dow;

    if (prev_hour(impl) == 0) {
        return 0;
    }

    if (!has_by_data(impl, ICAL_BY_DAY)) {
        return 1;
    }

    /* If we get here, we need to step to the previous day */

    impl->bydata[ICAL_BY_DAY].index--; /* Look at previous elem in BYDAY array */

    /* Are we at the end of the BYDAY array? */
    if (impl->bydata[ICAL_BY_DAY].index < 0) {
        impl->bydata[ICAL_BY_DAY].index = impl->bydata[ICAL_BY_DAY].by.size - 1;
        end_of_data = 1; /* Signal that we're at the end */
    }

    /* Add the day of week offset to the start of this week, and use
       that to get the next day */
    /* ignore position of dow ("4FR"), only use dow ("FR") */
    dow = (int)icalrecurrencetype_day_day_of_week(impl->bydata[ICAL_BY_DAY].by.data[impl->bydata[ICAL_BY_DAY].index]);
    dow -= (int)impl->rule->week_start; /* Set Sunday to be 0 */
    if (dow < 0) {
        dow += 7;
    }

    start_of_week = get_start_of_week(impl);

    if (dow + start_of_week < 1) {
        /* The selected date is in the previous year. */
        increment_year(impl, -1);
    }

    set_day_of_year(impl, start_of_week + dow);

    return end_of_data;
}

static int prev_week(icalrecur_iterator *impl)
{
    /* Decrement to the previous week day,
       if there is data at a level less than a week */
    if (prev_weekday_by_week(impl) == 0) {
        return 0; /* Have not reached start of week yet */
    }

    /* If we get here, we have decremented through the entire week, and
       can decrement to the previous week */

    /* Jump to the previous week */
    increment_monthday(impl, 7 * -impl->rule->interval);

    return 1;
}

/* For INTERVAL=YEARLY, set up the year days bitmask in the iterator to
   list all of the days of the current year that are specified in this
   rule. */
static void expand_year_days(icalrecur_iterator *impl, int year)
{
    int i;
    short days_in_year = (short)get_days_in_year(impl, year);
    short doy;

    daysmask_clearall(impl->days);

    /* We may end up skipping fwd/bwd a year during expansion.
       Mark our current start date so next_year() can increment from here */
    impl->period_start = occurrence_as_icaltime(impl, 0);

    if (has_by_data(impl, ICAL_BY_YEAR_DAY)) {
        /* We only support BYYEARDAY + BYDAY */
        if (has_by_data(impl, ICAL_BY_WEEK_NO) ||
            has_by_data(impl, ICAL_BY_MONTH) || has_by_data(impl, ICAL_BY_MONTH_DAY)) {
            icalerror_set_errno(ICAL_UNIMPLEMENTED_ERROR);
            return;
        }

        /* Add each BYYEARDAY to the year days bitmask */
        for (i = 0; i < impl->bydata[ICAL_BY_YEAR_DAY].by.size; i++) {
            doy = impl->bydata[ICAL_BY_YEAR_DAY].by.data[i];

            if (abs(doy) > days_in_year) {
                switch (impl->rule->skip) {
                default:
                    /* Should never get here! */

                case ICAL_SKIP_OMIT:
                    /* Invalid day */
                    continue;

                case ICAL_SKIP_FORWARD:
                    if (doy < 0) {
                        doy = 1; /* First day of this year */
                    } else {
                        doy = days_in_year + 1; /* First day of next year */
                    }
                    break;

                case ICAL_SKIP_BACKWARD:
                    if (doy < 0) {
                        doy = 0; /* Last day of prev year */
                    } else {
                        doy = days_in_year; /* Last day of this year */
                    }
                    break;
                }
            } else if (doy < 0) {
                doy += days_in_year + 1;
            }

            daysmask_setbit(impl->days, doy, 1);
            if (doy < impl->days_index) {
                impl->days_index = doy;
            }
        }
    } else if (has_by_data(impl, ICAL_BY_WEEK_NO)) {
        int weekno;

        /* We only support BYWEEKNO + BYDAY */
        if (has_by_data(impl, ICAL_BY_YEAR_DAY) ||
            has_by_data(impl, ICAL_BY_MONTH_DAY) ||
            (has_by_data(impl, ICAL_BY_MONTH) && !has_by_data(impl, ICAL_BY_DAY))) {
            icalerror_set_errno(ICAL_UNIMPLEMENTED_ERROR);
            return;
        }

        /* BYWEEKNO + BYDAY handled below */
        if (!has_by_data(impl, ICAL_BY_DAY)) {
            int nweeks = weeks_in_year(year);

            int start_doy = 1;
            /* See which week contains Jan 1 */
            (void)__icaltime_from_day_of_year(impl, 1, year, &weekno);
            if (weekno > 1) {
                /* Jan 1 is in last week of previous year - jump ahead */
                start_doy += 7;
            }
            /* Get the first day of the first week,
             * accounting for the week start */
            set_day_of_year(impl, 1);
            start_doy += get_start_of_week(impl) - 1;
            /* Adjust to the next instance of DTSTART's week day */
            start_doy += (get_day_of_week_adjusted(impl, impl->dtstart.year,
                                                   impl->dtstart.month, impl->dtstart.day) -
                          (int)impl->rule->week_start + 7) %
                         7;
            /* Reset impl to this year */
            (void)get_days_in_year(impl, year);

            /* Add day of week in each BYWEEKNO to the year days bitmask */
            for (i = 0; i < impl->bydata[ICAL_BY_WEEK_NO].by.size; i++) {
                weekno = impl->bydata[ICAL_BY_WEEK_NO].by.data[i];

                if (weekno < 0) {
                    weekno += nweeks + 1;
                } else if (weekno > nweeks) {
                    continue;
                }

                doy = start_doy + 7 * (weekno - 1);

                daysmask_setbit(impl->days, doy, 1);
                if (doy < impl->days_index) {
                    impl->days_index = doy;
                }
            }
        }
    } else {
        /* Add each BYMONTHDAY in each BYMONTH to the year days bitmask */
        for (i = 0; i < impl->bydata[ICAL_BY_MONTH].by.size; i++) {
            int month = set_month(impl, impl->bydata[ICAL_BY_MONTH].by.data[i]);

            if (month > 0 && month < ICAL_BY_MONTH_SIZE) {
                expand_bymonth_days(impl, year, month);
            }
        }
    }

    if (has_by_data(impl, ICAL_BY_DAY)) {
        /* Apply each BYDAY to the year days bitmask */
        int limiting =
            has_by_data(impl, ICAL_BY_YEAR_DAY) || has_by_data(impl, ICAL_BY_MONTH_DAY);
        int first_dow, last_dow;

        impl->days_index = ICAL_YEARDAYS_MASK_SIZE;

        if (has_by_data(impl, ICAL_BY_MONTH)) {
            /* Numeric BYDAY are within each month */

            for (i = 0; i < impl->bydata[ICAL_BY_MONTH].by.size; i++) {
                short month = impl->bydata[ICAL_BY_MONTH].by.data[i];
                if (month > 0 && month < ICAL_BY_MONTH_SIZE) {
                    int doy_offset, days_in_month;

                    /* Get offset within year & day of week of first day of month */
                    doy_offset =
                        get_day_of_year(impl, year, month, 1) - 1;
                    first_dow = get_day_of_week_adjusted(impl, year, month, 1);

                    /* Get day of week of last day of month */
                    days_in_month = get_days_in_month(impl, month, year);
                    last_dow = get_day_of_week_adjusted(impl, year,
                                                        month, days_in_month);

                    expand_by_day(impl, year, doy_offset, days_in_month,
                                  first_dow, last_dow, limiting);
                }
            }
        } else {
            /* Numeric BYDAY are within the year */
            short doy_offset = 0, last_day;

            if (has_by_data(impl, ICAL_BY_WEEK_NO)) {
                int weekno;

                /* See which week contains Jan 1 */
                (void)__icaltime_from_day_of_year(impl, 1, year, &weekno);
                if (weekno > 1) {
                    /* Jan 1 is in last week of previous year - jump ahead */
                    doy_offset += 7;
                }

                /* Set start and end of ISO week-numbering year */
                set_day_of_year(impl, 1);
                doy_offset += get_start_of_week(impl) - 1;
                last_day = (7 * weeks_in_year(year)) - doy_offset - 1;

                first_dow = (int)impl->rule->week_start;
                last_dow = (first_dow + 6) % 7;
            } else {
                /* Get day of week of first day of year */
                first_dow = get_day_of_week_adjusted(impl, year, 1, 1);

                /* Get day of week of last day of year */
                set_day_of_year(impl, days_in_year);
                last_dow = get_day_of_week(impl);

                last_day = days_in_year;
            }

            expand_by_day(impl, year, doy_offset, last_day, first_dow, last_dow, limiting);
        }
    }
}

static void __next_year(icalrecur_iterator *impl, int inc)
{
    struct icaltimetype this;

    /* Increment to and expand the next year */
    increment_year(impl, inc);
    this = occurrence_as_icaltime(impl, 0);
    expand_year_days(impl, this.year);
}

static int next_year(icalrecur_iterator *impl)
{
    return next_yearday(impl, &__next_year);
}

static int prev_year(icalrecur_iterator *impl)
{
    return prev_yearday(impl, &__next_year);
}

static short daymask_find_next_bit(const unsigned long *days, short start_index)
{
    short days_index = start_index;
    unsigned long v;
    short startBitIndex;
    unsigned short wordIdx;

    if (days_index >= ICAL_YEARDAYS_MASK_SIZE) {
        return ICAL_YEARDAYS_MASK_SIZE;
    }

    // Prepare the first word, where searching might not start at the beginning
    startBitIndex = days_index + ICAL_YEARDAYS_MASK_OFFSET;
    wordIdx = (unsigned short)(startBitIndex / BITS_PER_LONG);
    v = days[wordIdx];
    if (startBitIndex >= 0) {
        v >>= startBitIndex % BITS_PER_LONG;
    } else {
        v <<= -startBitIndex % BITS_PER_LONG;
    }

    if (!v) {
        // so the first word didn't contain any bits of interest.
        days_index += BITS_PER_LONG - startBitIndex % BITS_PER_LONG;

        // Are there more empty words following? Skip them.
        unsigned short maxWordIdx = (unsigned short)(LONGS_PER_BITS(ICAL_YEARDAYS_MASK_SIZE)) - 1;
        while (days_index < ICAL_YEARDAYS_MASK_SIZE && wordIdx < maxWordIdx) {
            wordIdx++;
            v = days[wordIdx];

            if (v) {
                break;
            }

            days_index += BITS_PER_LONG;
        }
    }

    if (v) {
        // We found a word containing the next bit but don't know the exact
        // position yet. Do a b-search to find it.

        unsigned long mask;
        int maskSize = (int)(BITS_PER_LONG / 2);
        mask = (((unsigned long)1) << maskSize) - 1;

        while (maskSize) {
            if ((v & mask) == 0) {
                v >>= maskSize;
                days_index += maskSize;
            }
            maskSize /= 2;
            mask >>= maskSize;
        }
    }

    return days_index;
}

static short daymask_find_prev_bit(const unsigned long *days, short start_index)
{
    short days_index = start_index;
    unsigned long v;
    short startBitIndex;
    int wordIdx;

    if (days_index <= -ICAL_YEARDAYS_MASK_OFFSET) {
        return -ICAL_YEARDAYS_MASK_OFFSET;
    }

    // Prepare the first word, where searching might not start at the beginning
    startBitIndex = days_index + ICAL_YEARDAYS_MASK_OFFSET;
    wordIdx = (int)(startBitIndex / BITS_PER_LONG);
    v = days[wordIdx];
    v <<= BITS_PER_LONG - (startBitIndex % BITS_PER_LONG) - 1;

    if (!v) {
        // so the first word didn't contain any bits of interest.
        days_index -= (startBitIndex % BITS_PER_LONG) + 1;

        // Are there more empty words leading? Skip them.
        while (days_index > -ICAL_YEARDAYS_MASK_OFFSET) {
            wordIdx--;
            v = days[wordIdx];

            if (v) {
                break;
            }

            days_index -= BITS_PER_LONG;
        }
    }

    if (v) {
        // We found a word containing the next bit but don't know the exact
        // position yet. Do a b-search to find it.

        unsigned long mask;
        int maskSize = (int)(BITS_PER_LONG / 2);
        mask = ((((unsigned long)1) << maskSize) - 1) << maskSize;

        while (maskSize) {
            if ((v & mask) == 0) {
                v <<= maskSize;
                days_index -= maskSize;
            }
            maskSize /= 2;
            /* coverity[integer_overflow] */
            mask <<= maskSize;
        }
    }

    return days_index;
}

static int next_yearday(icalrecur_iterator *impl,
                        void (*next_period)(icalrecur_iterator *, int))
{
    if (next_hour(impl) == 0) {
        return 0;
    }

    /* We may have skipped fwd/bwd a month/year with previous occurrence.
       Reset the period start date so we can increment properly */
    reset_period_start(impl);

    /* Find next year day that is set */
    impl->days_index = daymask_find_next_bit(impl->days, impl->days_index + 1);

    int ret = 0;

    if (impl->days_index >= ICAL_YEARDAYS_MASK_SIZE) {
        ret = 1;
        if (next_period) {
            for (;;) {
                /* Increment to and expand the next period */
                next_period(impl, impl->rule->interval);

                if (impl->days_index < ICAL_YEARDAYS_MASK_SIZE) {
                    break; /* break when a matching day is found */
                }
            }
        } else {
            /* When next_period is NULL,
               we only indicate that we have
               reached the end of the period */
            return 1;
        }
    }

    if (impl->days_index < 1) {
        /* Day is in previous year */
        increment_year(impl, -1);
    }

    set_day_of_year(impl, impl->days_index);

    return ret;
}

static int prev_yearday(icalrecur_iterator *impl,
                        void (*next_period)(icalrecur_iterator *, int))
{
    if (prev_hour(impl) == 0) {
        return 0;
    }

    /* We may have skipped fwd/bwd a month/year with previous occurrence.
       Reset the period start date so we can decrement properly */
    reset_period_start(impl);

    /* Find previous year day that is set */
    impl->days_index = daymask_find_prev_bit(impl->days, impl->days_index - 1);

    int ret = 0;

    while (impl->days_index <= -ICAL_YEARDAYS_MASK_OFFSET) {
        if (next_period) {
            ret = 1;
            /* Decrement to and expand the previous period */
            next_period(impl, -impl->rule->interval);

            impl->days_index = ICAL_YEARDAYS_MASK_SIZE;
            impl->days_index = daymask_find_prev_bit(impl->days, impl->days_index - 1);
        } else {
            /* When next_period is NULL,
               we only indicate that we have
               reached the end of the period */
            return 1;
        }
    }

    if (impl->days_index < 1) {
        /* Day is in previous year */
        increment_year(impl, -1);
    }

    set_day_of_year(impl, impl->days_index);

    return ret;
}

static int days_in_current_month(icalrecur_iterator *impl)
{
    return get_days_in_month(impl, impl->last.month, impl->last.year);
}

static int days_in_current_year(icalrecur_iterator *impl)
{
    return get_days_in_year(impl, impl->last.year);
}

static inline int has_contract_restriction(icalrecur_iterator *impl,
                                           icalrecurrencetype_byrule byrule)
{
    return impl->bydata[byrule].by.size > 0 &&
           expand_map[impl->rule->freq].map[byrule] == CONTRACT;
}

static bool check_contract_restriction(icalrecur_iterator *impl,
                                       icalrecurrencetype_byrule byrule, int v,
                                       int (*get_total)(icalrecur_iterator *))
{
    if (has_contract_restriction(impl, byrule)) {
        int total = 0;
        bool pass = false;
        for (int itr = 0; itr < impl->bydata[byrule].by.size; itr++) {
            short byval = impl->bydata[byrule].by.data[itr];
            if ((byval < 0) && (total == 0)) {
                if (get_total) {
                    // load total value lazily only when needed
                    total = get_total(impl);
                } else {
                    // limiting by negative values is only allowed for
                    // BYMONTHDAY, BYYEARDAY (BYDAY is handled separately)
                    icalerror_set_errno(ICAL_MALFORMEDDATA_ERROR);
                    continue;
                }
            }

            if (v == ((byval >= 0) ? byval : (total + 1 + byval))) {
                pass = true;
                break;
            }
        }

        return pass;
    }

    /* This is not a contracting byrule, or it has no data, so the test passes */
    return true;
}

static bool check_contracting_rules(icalrecur_iterator *impl)
{
    struct icaltimetype last = occurrence_as_icaltime(impl, 0);

// Check `has_contract_restriction` before calling `check_contract_restriction` to avoid
// evaluating potentially expensive `v` if not needed.
#define CHECK_CONTRACT_RESTRICTION(by, v, get_total) \
    (!has_contract_restriction(impl, (by)) || check_contract_restriction(impl, (by), (v), (get_total)))

    if (
        CHECK_CONTRACT_RESTRICTION(ICAL_BY_SECOND, last.second, NULL) &&
        CHECK_CONTRACT_RESTRICTION(ICAL_BY_MINUTE, last.minute, NULL) &&
        CHECK_CONTRACT_RESTRICTION(ICAL_BY_HOUR, last.hour, NULL) &&
        CHECK_CONTRACT_RESTRICTION(ICAL_BY_MONTH_DAY, last.day, days_in_current_month) &&
        CHECK_CONTRACT_RESTRICTION(ICAL_BY_MONTH, last.month, NULL) &&
        CHECK_CONTRACT_RESTRICTION(ICAL_BY_WEEK_NO, get_week_number(impl, last), NULL) &&
        CHECK_CONTRACT_RESTRICTION(
            ICAL_BY_DAY, get_day_of_week_adjusted(impl, last.year, last.month, last.day), NULL) &&
        CHECK_CONTRACT_RESTRICTION(
            ICAL_BY_YEAR_DAY, get_day_of_year(impl, last.year, last.month, last.day), days_in_current_year)) {
        return true;
    }

#undef CHECK_CONTRACT_RESTRICTION

    return false;
}

/* Initialize data relating to BYSETPOS, in particular:
 * set_pos, sp_idxp, sp_idxn, and recurrence_set_size.
 * This must be called at the start of each new period
 *
 * next == 1 indicates we are advancing the iterator,
 * and so are at the start of a new period, while
 * next == 0 indicates we are at the end of one
 */
static void setup_setpos(icalrecur_iterator *impl, int next)
{
    /* Save data that may be modified */
    int days_index = impl->days_index;
    int bydata_indices[ICAL_BY_NUM_PARTS];
    for (int byrule = 0; byrule < ICAL_BY_NUM_PARTS; byrule++) {
        bydata_indices[byrule] = impl->bydata[byrule].index;
    }
    struct icaltimetype last = impl->last;

    impl->recurrence_set_size = 1;
    int period_change = 1;
    do {
        switch (impl->rule->freq) {
        case ICAL_SECONDLY_RECURRENCE:
            break;
        case ICAL_MINUTELY_RECURRENCE:
            /* call next_second instead of next_minute
             * to avoid going to the next minute */
            period_change = (next ? next_second : prev_second)(impl);
            break;
        case ICAL_HOURLY_RECURRENCE:
            period_change = (next ? next_minute : prev_minute)(impl);
            break;
        case ICAL_DAILY_RECURRENCE:
            period_change = (next ? next_hour : prev_hour)(impl);
            break;
        case ICAL_WEEKLY_RECURRENCE:
            period_change = (next ? next_weekday_by_week : prev_weekday_by_week)(impl);
            break;
        case ICAL_MONTHLY_RECURRENCE:
            /* call next_yearday instead of next_month
             * to avoid expanding month days */
            period_change = (next ? next_yearday : prev_yearday)(impl, NULL);
            break;
        case ICAL_YEARLY_RECURRENCE:
            period_change = (next ? next_yearday : prev_yearday)(impl, NULL);
            break;
        default:
            icalerror_set_errno(ICAL_MALFORMEDDATA_ERROR);
            return;
        }
        if (period_change == 0 && check_contracting_rules(impl)) {
            impl->recurrence_set_size++;
        }
    } while (period_change == 0);

    if (next) {
        impl->set_pos = 1;
        impl->sp_idxp = 0;
        impl->sp_idxn = impl->bydata[ICAL_BY_SET_POS].by.size - 1;
    } else {
        impl->set_pos = impl->recurrence_set_size;
        impl->sp_idxp = impl->sp_pmax;
        impl->sp_idxn = impl->sp_pmax + 1;
    }

    /* Restore what was modified
     * Because we do not expand month/year days,
     * the days bitfield is not modified */
    set_datetime(impl, last);
    impl->last = last;
    impl->days_index = days_index;
    for (int byrule = 0; byrule < ICAL_BY_NUM_PARTS; byrule++) {
        impl->bydata[byrule].index = bydata_indices[byrule];
    }
}

/* If s1 occurs before s2 in the recurrence set, return -1
 * If s1 occurs after, return 1
 * If they are equal, return 0
 */
static inline int setpos_cmp(int s1, int s2, int next)
{
    if (s1 < s2) {
        return (next ? -1 : 1);
    } else if (s2 < s1) {
        return (next ? 1 : -1);
    }
    return 0;
}

/* Check whether impl->set_pos is a valid recurrence set position
 *
 * next == 1 indicates that we should increase and decrease
 * sp_idxp and sp_idxn, respectively, while
 * next == 0 indicates that we should decrease and increase them
 */
static bool check_setpos(icalrecur_iterator *impl, int next)
{
    if (!has_by_data(impl, ICAL_BY_SET_POS)) {
        return true;
    }
    icalrecurrence_by_data *by = &(impl->bydata[ICAL_BY_SET_POS].by);
    int32_t set_pos;

    /* If we have positive BYSETPOS data */
    if (impl->sp_pmax >= 0) {
        set_pos = by->data[impl->sp_idxp];
        /* Increment positive index while set_pos is before impl->set_pos */
        while (setpos_cmp(set_pos, impl->set_pos, next) < 0) {
            if (next && impl->sp_idxp < impl->sp_pmax) {
                impl->sp_idxp++;
            } else if (!next && impl->sp_idxp > 0) {
                impl->sp_idxp--;
            } else {
                break;
            }
            set_pos = by->data[impl->sp_idxp];
        }
        if (impl->set_pos == set_pos) {
            return true;
        }
    }

    if (impl->sp_pmax < by->size - 1) {
        set_pos = by->data[impl->sp_idxn] + impl->recurrence_set_size + 1;
        while (setpos_cmp(set_pos, impl->set_pos, next) < 0) {
            if (next && impl->sp_idxn > impl->sp_pmax + 1) {
                impl->sp_idxn--;
            } else if (!next && impl->sp_idxn < by->size - 1) {
                impl->sp_idxn++;
            } else {
                break;
            }
            set_pos = by->data[impl->sp_idxn] + impl->recurrence_set_size + 1;
        }
        if (impl->set_pos == set_pos) {
            return true;
        }
    }
    return false;
}

struct icaltimetype icalrecur_iterator_next(icalrecur_iterator *impl)
{
    /* Quit if we reached COUNT or if last time is after the UNTIL time */
    if (!impl ||
        (impl->rule->count != 0 && impl->occurrence_no >= impl->rule->count) ||
        (!icaltime_is_null_time(impl->rule->until) &&
         icaltime_compare(impl->last, impl->rule->until) > 0)) {
        return icaltime_null_time();
    }

    /* If initial time is valid, return it */
    if ((impl->occurrence_no == 0) &&
        (icaltime_compare(impl->last, impl->istart) >= 0) &&
        check_setpos(impl, 1) &&
        check_contracting_rules(impl)) {
        impl->occurrence_no++;
        return impl->last;
    }

    int period_change = 1;
    /* store previous instance, including iterator structures
     * (e.g., bydata) */
    icalrecur_iterator impl_last = *impl;

    /* Iterate until we get the next valid time */
    size_t stalledCnt = 0;
    const size_t max_recurrence_time_count = icallimit_get(ICAL_LIMIT_RECURRENCE_TIME_STANDING_STILL);
    int lastTimeCompare = 0;
    bool hasByData = false;
    int checkContractingRules = 0;
    size_t cntRecurrences = 0;
    const size_t max_recurrences = icallimit_get(ICAL_LIMIT_RECURRENCE_SEARCH);
    do {
        switch (impl->rule->freq) {
        case ICAL_SECONDLY_RECURRENCE:
            /* period_change is always true for secondly recurrence */
            next_second(impl);
            break;

        case ICAL_MINUTELY_RECURRENCE:
            period_change = next_minute(impl);
            break;

        case ICAL_HOURLY_RECURRENCE:
            period_change = next_hour(impl);
            break;

        case ICAL_DAILY_RECURRENCE:
            period_change = next_day(impl);
            break;

        case ICAL_WEEKLY_RECURRENCE:
            period_change = next_week(impl);
            break;

        case ICAL_MONTHLY_RECURRENCE:
            period_change = next_month(impl);
            break;

        case ICAL_YEARLY_RECURRENCE:
            period_change = next_year(impl);
            break;

        default:
            icalerror_set_errno(ICAL_MALFORMEDDATA_ERROR);
            return icaltime_null_time();
        }

        impl->last = occurrence_as_icaltime(impl, 1);

        /* Ignore times that are after the MAX year,
           or the UNTIL time, or the end time */
        if (impl->last.year > MAX_TIME_T_YEAR ||
            (!icaltime_is_null_time(impl->rule->until) &&
             icaltime_compare(impl->last, impl->rule->until) > 0) ||
            (!icaltime_is_null_time(impl->iend) &&
             icaltime_compare(impl->last, impl->iend) >= 0)) {
            /* reset to valid instance */
            *impl = impl_last;
            set_datetime(impl, impl_last.last);
            return icaltime_null_time();
        }

        hasByData = has_by_data(impl, ICAL_BY_SET_POS);
        checkContractingRules = -1;
        if (hasByData) {
            checkContractingRules = check_contracting_rules(impl) ? 1 : 0;
            if (checkContractingRules == 1) {
                if (period_change) {
                    setup_setpos(impl, 1);
                } else {
                    impl->set_pos++;
                }
            }
        }

        // is time standing still? if so, break out of here
        lastTimeCompare = icaltime_compare(impl->last, impl_last.last);
        if (lastTimeCompare == 0) {
            if (stalledCnt++ == max_recurrence_time_count) {
                break;
            }
        } else {
            stalledCnt = 0;
        }
    } while ((cntRecurrences++ < max_recurrences) &&
             ((lastTimeCompare == 0) ||
              (hasByData && !check_setpos(impl, 1)) ||
              icaltime_compare(impl->last, impl->istart) < 0 ||
              (checkContractingRules == 0) ||
              (checkContractingRules == -1 && !check_contracting_rules(impl))));

    impl->occurrence_no++;

    return impl->last;
}

struct icaltimetype icalrecur_iterator_prev(icalrecur_iterator *impl)
{
    /* Quit if last time is before the DTSTART time */
    if (!impl || icaltime_compare(impl->last, impl->dtstart) < 0) {
        return icaltime_null_time();
    }

    int period_change = 1;
    icalrecur_iterator impl_last = *impl;

    /* Iterate until we get the next valid time */
    do {
        switch (impl->rule->freq) {
        case ICAL_SECONDLY_RECURRENCE:
            prev_second(impl);
            break;

        case ICAL_MINUTELY_RECURRENCE:
            period_change = prev_minute(impl);
            break;

        case ICAL_HOURLY_RECURRENCE:
            period_change = prev_hour(impl);
            break;

        case ICAL_DAILY_RECURRENCE:
            period_change = prev_day(impl);
            break;

        case ICAL_WEEKLY_RECURRENCE:
            period_change = prev_week(impl);
            break;

        case ICAL_MONTHLY_RECURRENCE:
            period_change = prev_month(impl);
            break;

        case ICAL_YEARLY_RECURRENCE:
            period_change = prev_year(impl);
            break;

        default:
            icalerror_set_errno(ICAL_MALFORMEDDATA_ERROR);
            return icaltime_null_time();
        }

        impl->last = occurrence_as_icaltime(impl, 1);

        /* Ignore times that are before the DTSTART time */
        if (icaltime_compare(impl->last, impl->dtstart) < 0 ||
            (!icaltime_is_null_time(impl->istart) &&
             icaltime_compare(impl->last, impl->istart) < 0)) {
            *impl = impl_last;
            set_datetime(impl, impl_last.last);
            return icaltime_null_time();
        }

        if (has_by_data(impl, ICAL_BY_SET_POS) && check_contracting_rules(impl)) {
            if (period_change) {
                setup_setpos(impl, 0);
            } else {
                impl->set_pos--;
            }
        }

    } while (impl->last.year > MAX_TIME_T_YEAR ||
             (!icaltime_is_null_time(impl->rule->until) &&
              icaltime_compare(impl->last, impl->rule->until) > 0) ||
             (!icaltime_is_null_time(impl->iend) &&
              icaltime_compare(impl->last, impl->iend) > 0) ||
             icaltime_compare(impl->last, impl_last.last) == 0 ||
             (has_by_data(impl, ICAL_BY_SET_POS) && !check_setpos(impl, 0)) ||
             !check_contracting_rules(impl));

    impl->occurrence_no--;

    return impl->last;
}

static void set_bydata_start(icalrecurrence_iterator_by_data *bydata, int tfield)
{
    int bdi;
    for (bdi = 0;
         bdi < bydata->by.size; bdi++) {
        if (bydata->by.data[bdi] == tfield) {
            bydata->index = bdi;
            return;
        }
    }
}

static bool __iterator_set_start(icalrecur_iterator *impl, icaltimetype start)
{
    icalrecurrencetype_frequency freq = impl->rule->freq;
    short interval = impl->rule->interval;
    int diff;

    impl->istart = start;
    impl->occurrence_no = 0;
    impl->days_index = ICAL_YEARDAYS_MASK_SIZE;

    /* Set Gregorian start date */
    set_start(impl, start);

    switch (freq) {
    case ICAL_YEARLY_RECURRENCE:
        /* For YEARLY rule, begin by setting up the year days array.
           The YEARLY rules work by expanding one year at a time. */

        if ((interval > 1) &&
            (diff = (impl->istart.year - impl->rstart.year) % interval)) {
            /* Specified start year doesn't match interval -
               bump start to first day of next year that matches interval */
            set_day_of_year(impl, 1);
            increment_year(impl, interval - diff);
        }

        /* Get (adjusted) start date as RSCALE date */
        start = occurrence_as_icaltime(impl, 0);

        if (has_by_data(impl, ICAL_BY_WEEK_NO)) {
            int start_weekno = get_week_number(impl, start);
            if (start_weekno > 5 &&
                start.month == 1) {
                /* if we are in the last week of the previous year,
                 * expand year days for the previous year
                 */
                increment_year(impl, -1);
                expand_year_days(impl, start.year - 1);
                int days_in_year = get_days_in_year(impl, start.year - 1);
                impl->days_index = daymask_find_next_bit(impl->days, days_in_year + 1);
                if (impl->days_index >= ICAL_YEARDAYS_MASK_SIZE) {
                    increment_year(impl, 1);
                }
            } else if (start_weekno < 45 &&
                       start.month == 12) {
                /* if we are in the first week of the next year,
                 * expand year days for the next year
                 */
                increment_year(impl, 1);
                expand_year_days(impl, start.year + 1);
                impl->days_index = daymask_find_next_bit(impl->days, -ICAL_YEARDAYS_MASK_OFFSET);
                if (impl->days_index >= ICAL_YEARDAYS_MASK_SIZE) {
                    increment_year(impl, -1);
                }
            }
        }

        /* Expand days array for (adjusted) start year -
           fail after hitting the year MAX_TIME_T_YEAR if no expanded days match */
        while (start.year < MAX_TIME_T_YEAR && impl->days_index >= ICAL_YEARDAYS_MASK_SIZE) {
            expand_year_days(impl, start.year);

            icalerrorenum err = icalerrno;
            switch (err) {
            case ICAL_NO_ERROR:
                break;
            case ICAL_UNIMPLEMENTED_ERROR:
                return false;
            default:
                icalerror_set_errno(ICAL_MALFORMEDDATA_ERROR);
                return false;
            }

            if (impl->days_index >= ICAL_YEARDAYS_MASK_SIZE) {
                increment_year(impl, interval);
                start = occurrence_as_icaltime(impl, 0);
            }
        }

        /* Copy the first day into last */
        set_day_of_year(impl, impl->days_index);
        if (impl->days_index < 1) {
            increment_year(impl, -1);
        }

        break;

    case ICAL_MONTHLY_RECURRENCE:
        /* For MONTHLY rule, begin by setting up the year days array.
           The MONTHLY rules work by expanding one month at a time. */

        if ((interval > 1) &&
            (diff = month_diff(impl, impl->rstart, impl->istart) % interval)) {
            /* Specified month doesn't match interval -
               bump start to first day of next month that matches interval */
            increment_monthday(impl, -impl->istart.day + 1);
            __increment_month(impl, interval - diff);
        }

        /* Get (adjusted) start date as RSCALE date */
        start = occurrence_as_icaltime(impl, 0);

        /* Expand days array for (adjusted) start month -
           fail after hitting the year 20000 if no expanded days match */
        while (start.year < 20000) {
            expand_month_days(impl, start.year, start.month);
            if (impl->days_index < ICAL_YEARDAYS_MASK_SIZE) {
                break; /* break when a matching day is found */
            }
            increment_month(impl, impl->rule->interval);
            start = occurrence_as_icaltime(impl, 0);
        }

        /* Copy the first day into last */
        set_day_of_year(impl, impl->days_index);

        break;

    case ICAL_WEEKLY_RECURRENCE:
        if (impl->bydata[ICAL_BY_DAY].by.size <= 0) {
            /* Weekly recurrences with no ICAL_BY_DAY data should occur on the
               same day of the week as the start time . */
            recur_iterator_set_static_single_by_value(impl, ICAL_BY_DAY, (short)get_day_of_week(impl));
        } else {
            adjust_to_byday(impl);

            /* If start == DTSTART, adjust rstart */
            if (icaltime_compare(start, impl->dtstart) == 0) {
                impl->rstart = occurrence_as_icaltime(impl, 0);
            }

            /* Get (adjusted) start date as RSCALE date */
            start = occurrence_as_icaltime(impl, 0);

            if ((interval > 1) &&
                (diff = (day_diff(impl, impl->rstart, start) + 6) / 7) % interval) {
                /* Specified week doesn't match interval -
                   bump start to next week that matches interval */
                increment_monthday(impl, 7 * (interval - diff));
            }
        }
        break;

    case ICAL_DAILY_RECURRENCE:
        if ((interval > 1) &&
            (diff = day_diff(impl, impl->rstart, impl->istart) % interval)) {
            /* Specified day doesn't match interval -
               bump start to next day that matches interval */
            increment_monthday(impl, interval - diff);
        }
        break;

    case ICAL_HOURLY_RECURRENCE:
        if ((interval > 1) &&
            (diff = abs(impl->istart.hour - impl->rstart.hour) % interval)) {
            /* Specified hour doesn't match interval -
               bump start to next hour that matches interval */
            increment_hour(impl, interval - diff);
        }
        set_bydata_start(&impl->bydata[ICAL_BY_HOUR], impl->istart.hour);
        break;

    case ICAL_MINUTELY_RECURRENCE:
        if ((interval > 1) &&
            (diff = abs(impl->istart.minute - impl->rstart.minute) % interval)) {
            /* Specified minute doesn't match interval -
               bump start to next minute that matches interval */
            increment_minute(impl, interval - diff);
        }
        set_bydata_start(&impl->bydata[ICAL_BY_MINUTE], impl->istart.minute);
        break;

    case ICAL_SECONDLY_RECURRENCE:
        if ((interval > 1) &&
            (diff = abs(impl->istart.second - impl->rstart.second) % interval)) {
            /* Specified second doesn't match interval -
               bump start to next second that matches interval */
            increment_second(impl, interval - diff);
        }
        set_bydata_start(&impl->bydata[ICAL_BY_SECOND], impl->istart.second);
        break;

    default:
        break;
    }

    /* Get start date as Gregorian date */
    impl->last = occurrence_as_icaltime(impl, 1);
    if (has_by_data(impl, ICAL_BY_SET_POS)) {
        setup_setpos(impl, 1);
    }

    /* Fail if first instance exceeds MAX_TIME_T_YEAR */
    if (impl->last.year > MAX_TIME_T_YEAR) {
        icalerror_set_errno(ICAL_MALFORMEDDATA_ERROR);
        return false;
    }

    return true;
}

bool icalrecur_iterator_set_start(icalrecur_iterator *impl,
                                  struct icaltimetype start)
{
    /* We can't adjust start date if we need to count occurrences */
    if (impl->rule->count > 0) {
        icalerror_set_errno(ICAL_MALFORMEDDATA_ERROR);
        return false;
    }

    /* Convert start to same time zone as DTSTART */
    start = icaltime_convert_to_zone(start, (icaltimezone *)impl->dtstart.zone);

    if (icaltime_compare(start, impl->dtstart) < 0) {
        /* If start is before DTSTART, use DTSTART */
        start = impl->dtstart;
    } else if (!icaltime_is_null_time(impl->rule->until) &&
               icaltime_compare(start, impl->rule->until) > 0) {
        /* If start is after UNTIL, we're done */
        impl->last = start;
        return true;
    }

    return __iterator_set_start(impl, start);
}

bool icalrecur_iterator_set_end(icalrecur_iterator *impl,
                                struct icaltimetype end)
{
    /* Convert end to same time zone as DTSTART */
    end = icaltime_convert_to_zone(end, (icaltimezone *)impl->dtstart.zone);

    impl->iend = end;

    return true;
}

bool icalrecur_iterator_set_range(icalrecur_iterator *impl,
                                  struct icaltimetype from,
                                  struct icaltimetype to)
{
    if (impl->rule->count > 0 || icaltime_is_null_time(from)) {
        /* Can't set a range without 'from' or if we need to count occurrences */
        icalerror_set_errno(ICAL_MALFORMEDDATA_ERROR);
        return false;
    }

    if (!icaltime_is_null_time(to) && icaltime_compare(to, from) < 0) {
        /* Setting up for the reverse iterator */
        const icaltimezone *zone = impl->dtstart.zone;

        /* Convert 'from' to same time zone as DTSTART */
        from = icaltime_convert_to_zone(from, (icaltimezone *)zone);

        if (icaltime_compare(from, impl->rule->until) > 0) {
            /* If 'from' is after UNTIL, use UNTIL */
            from = impl->rule->until;
        } else if (icaltime_compare(from, impl->dtstart) < 0) {
            /* If 'from' is before START, we're done */
            impl->last = from;
            return true;
        }

        if (!__iterator_set_start(impl, from)) {
            return false;
        }

        /* __iterator_set_start() may back us up earlier than 'from'
           Iterate forward until we are later than 'from'.
        */
        while (icaltime_compare(impl->last, from) < 0) {
            (void)icalrecur_iterator_next(impl);
        }

        /* Convert 'to' to same time zone as DTSTART */
        to = icaltime_convert_to_zone(to, (icaltimezone *)zone);

        if (icaltime_compare(to, impl->dtstart) < 0) {
            /* If 'to' is before DTSTART, use DTSTART */
            to = impl->dtstart;
        }

        impl->istart = to;
        impl->iend = from;
        impl->days_index = 0;
    } else {
        if (!icalrecur_iterator_set_start(impl, from)) {
            return false;
        }

        icalrecur_iterator_set_end(impl, to);
    }

    return true;
}

/************************** Type Routines **********************/

static void icalrecurrencetype_clear(struct icalrecurrencetype *recur)
{
    int refcount = recur->refcount;

    icalrecurrencetype_free(recur, 0);

    memset(recur, 0, sizeof(*recur));

    recur->refcount = refcount;

    recur->week_start = ICAL_MONDAY_WEEKDAY;
    recur->freq = ICAL_NO_RECURRENCE;
    recur->interval = 1;
    recur->until = icaltime_null_time();
    recur->count = 0;
    recur->rscale = NULL;
    recur->skip = ICAL_SKIP_OMIT;
}

enum icalrecurrencetype_weekday icalrecurrencetype_day_day_of_week(short day)
{
    return (enum icalrecurrencetype_weekday)(abs(day) % 8);
}

int icalrecurrencetype_day_position(short day)
{
    int wd, pos;

    wd = (int)icalrecurrencetype_day_day_of_week(day);

    pos = (abs(day) - wd) / 8 * ((day < 0) ? -1 : 1);

    return pos;
}

short icalrecurrencetype_encode_day(enum icalrecurrencetype_weekday weekday, int position)
{
    short s_weekday = (short)weekday;
    short a_position = (short)(8 * abs(position));
    return (s_weekday + a_position) * ((position < 0) ? -1 : 1);
}

bool icalrecurrencetype_month_is_leap(short month)
{
    return (month & LEAP_MONTH);
}

int icalrecurrencetype_month_month(short month)
{
    return (month & ~LEAP_MONTH);
}

short icalrecurrencetype_encode_month(int month, bool is_leap)
{
    return (short)month | (is_leap ? LEAP_MONTH : 0);
}

bool icalrecur_expand_recurrence(const char *rule,
                                 icaltime_t start, int count, icaltime_t *array)
{
    struct icalrecurrencetype *recur;
    icalrecur_iterator *ritr;
    struct icaltimetype icstart;

    memset(array, 0, (size_t)count * sizeof(icaltime_t));

    icstart = icaltime_from_timet_with_zone(start, 0, 0);

    recur = icalrecurrencetype_new_from_string(rule);
    if (!recur) {
        return false;
    }

    ritr = icalrecur_iterator_new(recur, icstart);
    if (ritr) {
        int i = 0;
        for (struct icaltimetype next = icalrecur_iterator_next(ritr);
             !icaltime_is_null_time(next) && i < count;
             next = icalrecur_iterator_next(ritr)) {
            icaltime_t tt = icaltime_as_timet(next);

            if (tt >= start) {
                array[i++] = tt;
            }
        }
        icalrecur_iterator_free(ritr);
    }

    icalrecurrencetype_unref(recur);

    return true;
}

ical_invalid_rrule_handling ical_get_invalid_rrule_handling_setting(void)
{
    ical_invalid_rrule_handling myHandling;

#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
    if (pthread_mutex_lock(&invalid_rrule_mutex) != 0) {
        icalerror_set_errno(ICAL_THREADING_ERROR);
    }
#endif

    myHandling = invalidRruleHandling;

#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
    if (pthread_mutex_unlock(&invalid_rrule_mutex) != 0) {
        icalerror_set_errno(ICAL_THREADING_ERROR);
    }
#endif

    return myHandling;
}

void ical_set_invalid_rrule_handling_setting(ical_invalid_rrule_handling newSetting)
{
#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
    if (pthread_mutex_lock(&invalid_rrule_mutex) != 0) {
        icalerror_set_errno(ICAL_THREADING_ERROR);
    }
#endif

    invalidRruleHandling = newSetting;

#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
    if (pthread_mutex_unlock(&invalid_rrule_mutex) != 0) {
        icalerror_set_errno(ICAL_THREADING_ERROR);
    }
#endif
}