[p5sagit/p5-mst-13.2.git] / localtime64.c

/*

Copyright (c) 2007-2008  Michael G Schwern

This software originally derived from Paul Sheer's pivotal_gmtime_r.c.

The MIT License:

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

*/

/*

Programmers who have available to them 64-bit time values as a 'long
long' type can use localtime64_r() and gmtime64_r() which correctly
converts the time even on 32-bit systems. Whether you have 64-bit time
values will depend on the operating system.

localtime64_r() is a 64-bit equivalent of localtime_r().

gmtime64_r() is a 64-bit equivalent of gmtime_r().

*/

#include "localtime64.h"

static const int days_in_month[2][12] = {
    {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
    {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
};

static const int julian_days_by_month[2][12] = {
    {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334},
    {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335},
};

static const int length_of_year[2] = { 365, 366 };

/* Number of days in a 400 year Gregorian cycle */
static const int years_in_gregorian_cycle = 400;
static const int days_in_gregorian_cycle  = (365 * 400) + 100 - 4 + 1;

/* 28 year calendar cycle between 2010 and 2037 */
static const int safe_years[28] = {
    2016, 2017, 2018, 2019,
    2020, 2021, 2022, 2023,
    2024, 2025, 2026, 2027,
    2028, 2029, 2030, 2031,
    2032, 2033, 2034, 2035,
    2036, 2037, 2010, 2011,
    2012, 2013, 2014, 2015
};

static const int dow_year_start[28] = {
    5, 0, 1, 2,     /* 2016 - 2019 */
    3, 5, 6, 0,
    1, 3, 4, 5,
    6, 1, 2, 3,
    4, 6, 0, 1,
    2, 4, 5, 6,     /* 2036, 2037, 2010, 2011 */
    0, 2, 3, 4      /* 2012, 2013, 2014, 2015 */
};

/* Let's assume people are going to be looking for dates in the future.
   Let's provide some cheats so you can skip ahead.
   This has a 4x speed boost when near 2008.
*/
/* Number of days since epoch on Jan 1st, 2008 GMT */
#define CHEAT_DAYS  (1199145600 / 24 / 60 / 60)
#define CHEAT_YEARS 108

#define IS_LEAP(n)	((!(((n) + 1900) % 400) || (!(((n) + 1900) % 4) && (((n) + 1900) % 100))) != 0)
#define WRAP(a,b,m)	((a) = ((a) <  0  ) ? ((b)--, (a) + (m)) : (a))

#define SHOULD_USE_SYSTEM_LOCALTIME(a)  ( USE_SYSTEM_LOCALTIME && (a) <= SYSTEM_LOCALTIME_MAX )
#define SHOULD_USE_SYSTEM_GMTIME(a)     ( USE_SYSTEM_GMTIME &&    (a) <= SYSTEM_GMTIME_MAX )


int _is_exception_century(Int64 year)
{
    int is_exception = ((year % 100 == 0) && !(year % 400 == 0));
    /* printf("is_exception_century: %s\n", is_exception ? "yes" : "no"); */

    return(is_exception);
}


/* timegm() is a GNU extension, so emulate it here if we need it */
#ifdef HAS_TIMEGM
#    define TIMEGM(n) timegm(n);
#else
#    define TIMEGM(n) _my_timegm(n);
#endif

time_t _my_timegm(struct tm *date) {
    int days    = 0;
    int seconds = 0;
    time_t time;
    int year;

    if( date->tm_year > 70 ) {
        year = 70;
        while( year < date->tm_year ) {
            days += length_of_year[IS_LEAP(year)];
            year++;
        }
    }
    else if ( date->tm_year < 70 ) {
        year = 69;
        do {
            days -= length_of_year[IS_LEAP(year)];
            year--;
        } while( year >= date->tm_year );
    }

    days += julian_days_by_month[IS_LEAP(date->tm_year)][date->tm_mon];
    days += date->tm_mday - 1;

    seconds += date->tm_hour * 60 * 60;
    seconds += date->tm_min * 60;
    seconds += date->tm_sec;

    time = (time_t)(days * 60 * 60 * 24) + seconds;

    return(time);
}


int _check_tm(struct tm *tm)
{
    /* Don't forget leap seconds */
    assert(tm->tm_sec >= 0);
    assert(tm->tm_sec <= 61);

    assert(tm->tm_min >= 0);
    assert(tm->tm_min <= 59);

    assert(tm->tm_hour >= 0);
    assert(tm->tm_hour <= 23);

    assert(tm->tm_mday >= 1);
    assert(tm->tm_mday <= days_in_month[IS_LEAP(tm->tm_year)][tm->tm_mon]);

    assert(tm->tm_mon  >= 0);
    assert(tm->tm_mon  <= 11);

    assert(tm->tm_wday >= 0);
    assert(tm->tm_wday <= 6);

    assert(tm->tm_yday >= 0);
    assert(tm->tm_yday <= length_of_year[IS_LEAP(tm->tm_year)]);

#ifdef HAS_TM_TM_GMTOFF
    assert(tm->tm_gmtoff >= -24 * 60 * 60);
    assert(tm->tm_gmtoff <=  24 * 60 * 60);
#endif

    return 1;
}


/* The exceptional centuries without leap years cause the cycle to
   shift by 16
*/
int _cycle_offset(Int64 year)
{
    const Int64 start_year = 2000;
    Int64 year_diff  = year - start_year - 1;
    Int64 exceptions  = year_diff / 100;
    exceptions     -= year_diff / 400;

    assert( year >= 2001 );

    /* printf("year: %d, exceptions: %d\n", year, exceptions); */

    return exceptions * 16;
}

/* For a given year after 2038, pick the latest possible matching
   year in the 28 year calendar cycle.
*/
#define SOLAR_CYCLE_LENGTH 28
int _safe_year(Int64 year)
{
    int safe_year;
    Int64 year_cycle = year + _cycle_offset(year);

    /* Change non-leap xx00 years to an equivalent */
    if( _is_exception_century(year) )
        year_cycle += 11;

    year_cycle %= SOLAR_CYCLE_LENGTH;

    safe_year = safe_years[year_cycle];

    assert(safe_year <= 2037 && safe_year >= 2010);

    /*
    printf("year: %d, year_cycle: %d, safe_year: %d\n",
           year, year_cycle, safe_year);
    */

    return safe_year;
}

struct tm *gmtime64_r (const Time64_T *in_time, struct tm *p)
{
    int v_tm_sec, v_tm_min, v_tm_hour, v_tm_mon, v_tm_wday;
    Int64 v_tm_tday;
    int leap;
    Int64 m;
    Time64_T time = *in_time;
    Int64 year = 70;

    /* Use the system gmtime() if time_t is small enough */
    if( SHOULD_USE_SYSTEM_GMTIME(*in_time) ) {
        time_t safe_time = *in_time;
        localtime_r(&safe_time, p);
        assert(_check_tm(p));
        return p;
    }

#ifdef HAS_TM_TM_GMTOFF
    p->tm_gmtoff = 0;
#endif
    p->tm_isdst  = 0;

#ifdef HAS_TM_TM_ZONE
    p->tm_zone   = "UTC";
#endif

    v_tm_sec =  time % 60;
    time /= 60;
    v_tm_min =  time % 60;
    time /= 60;
    v_tm_hour = time % 24;
    time /= 24;
    v_tm_tday = time;
    WRAP (v_tm_sec, v_tm_min, 60);
    WRAP (v_tm_min, v_tm_hour, 60);
    WRAP (v_tm_hour, v_tm_tday, 24);
    if ((v_tm_wday = (v_tm_tday + 4) % 7) < 0)
        v_tm_wday += 7;
    m = v_tm_tday;

    if (m >= CHEAT_DAYS) {
        year = CHEAT_YEARS;
        m -= CHEAT_DAYS;
    }

    if (m >= 0) {
        /* Gregorian cycles, this is huge optimization for distant times */
        while (m >= (Time64_T) days_in_gregorian_cycle) {
            m -= (Time64_T) days_in_gregorian_cycle;
            year += years_in_gregorian_cycle;
        }

        /* Years */
        leap = IS_LEAP (year);
        while (m >= (Time64_T) length_of_year[leap]) {
            m -= (Time64_T) length_of_year[leap];
            year++;
            leap = IS_LEAP (year);
        }

        /* Months */
        v_tm_mon = 0;
        while (m >= (Time64_T) days_in_month[leap][v_tm_mon]) {
            m -= (Time64_T) days_in_month[leap][v_tm_mon];
            v_tm_mon++;
        }
    } else {
        year--;

        /* Gregorian cycles */
        while (m < (Time64_T) -days_in_gregorian_cycle) {
            m += (Time64_T) days_in_gregorian_cycle;
            year -= years_in_gregorian_cycle;
        }

        /* Years */
        leap = IS_LEAP (year);
        while (m < (Time64_T) -length_of_year[leap]) {
            m += (Time64_T) length_of_year[leap];
            year--;
            leap = IS_LEAP (year);
        }

        /* Months */
        v_tm_mon = 11;
        while (m < (Time64_T) -days_in_month[leap][v_tm_mon]) {
            m += (Time64_T) days_in_month[leap][v_tm_mon];
            v_tm_mon--;
        }
        m += (Time64_T) days_in_month[leap][v_tm_mon];
    }

    p->tm_year = year;
    if( p->tm_year != year ) {
#ifdef EOVERFLOW
        errno = EOVERFLOW;
#endif
        return NULL;
    }

    p->tm_mday = (int) m + 1;
    p->tm_yday = julian_days_by_month[leap][v_tm_mon] + m;
    p->tm_sec = v_tm_sec, p->tm_min = v_tm_min, p->tm_hour = v_tm_hour,
        p->tm_mon = v_tm_mon, p->tm_wday = v_tm_wday;

    assert(_check_tm(p));

    return p;
}


struct tm *localtime64_r (const Time64_T *time, struct tm *local_tm)
{
    time_t safe_time;
    struct tm gm_tm;
    Int64 orig_year;
    int month_diff;

    /* Use the system localtime() if time_t is small enough */
    if( SHOULD_USE_SYSTEM_LOCALTIME(*time) ) {
        safe_time = *time;
        localtime_r(&safe_time, local_tm);
        assert(_check_tm(local_tm));
        return local_tm;
    }

    gmtime64_r(time, &gm_tm);
    orig_year = gm_tm.tm_year;

    if (gm_tm.tm_year > (2037 - 1900))
        gm_tm.tm_year = _safe_year(gm_tm.tm_year + 1900) - 1900;

    safe_time = TIMEGM(&gm_tm);
    localtime_r(&safe_time, local_tm);

    local_tm->tm_year = orig_year;
    month_diff = local_tm->tm_mon - gm_tm.tm_mon;

    /*  When localtime is Dec 31st previous year and
        gmtime is Jan 1st next year.
    */
    if( month_diff == 11 ) {
        local_tm->tm_year--;
    }

    /*  When localtime is Jan 1st, next year and
        gmtime is Dec 31st, previous year.
    */
    if( month_diff == -11 ) {
        local_tm->tm_year++;
    }

    /* GMT is Jan 1st, xx01 year, but localtime is still Dec 31st
       in a non-leap xx00.  There is one point in the cycle
       we can't account for which the safe xx00 year is a leap
       year.  So we need to correct for Dec 31st comming out as
       the 366th day of the year.
    */
    if( !IS_LEAP(local_tm->tm_year) && local_tm->tm_yday == 365 )
        local_tm->tm_yday--;

    assert(_check_tm(local_tm));

    return local_tm;
}
Commit	Line	Data
a272e669	1	/*
	2
	3	Copyright (c) 2007-2008 Michael G Schwern
	4
	5	This software originally derived from Paul Sheer's pivotal_gmtime_r.c.
	6
	7	The MIT License:
	8
	9	Permission is hereby granted, free of charge, to any person obtaining a copy
	10	of this software and associated documentation files (the "Software"), to deal
	11	in the Software without restriction, including without limitation the rights
	12	to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	13	copies of the Software, and to permit persons to whom the Software is
	14	furnished to do so, subject to the following conditions:
	15
	16	The above copyright notice and this permission notice shall be included in
	17	all copies or substantial portions of the Software.
	18
	19	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	20	IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	21	FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	22	AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	23	LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	24	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
	25	THE SOFTWARE.
	26
	27	*/
	28
	29	/*
	30
	31	Programmers who have available to them 64-bit time values as a 'long
	32	long' type can use localtime64_r() and gmtime64_r() which correctly
	33	converts the time even on 32-bit systems. Whether you have 64-bit time
	34	values will depend on the operating system.
	35
	36	localtime64_r() is a 64-bit equivalent of localtime_r().
	37
	38	gmtime64_r() is a 64-bit equivalent of gmtime_r().
	39
	40	*/
	41
af9b2bf5	42	#include "localtime64.h"
af9b2bf5	43
a272e669	44	static const int days_in_month[2][12] = {
	45	{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
	46	{31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
	47	};
	48
	49	static const int julian_days_by_month[2][12] = {
	50	{0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334},
	51	{0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335},
	52	};
	53
	54	static const int length_of_year[2] = { 365, 366 };
	55
	56	/* Number of days in a 400 year Gregorian cycle */
	57	static const int years_in_gregorian_cycle = 400;
	58	static const int days_in_gregorian_cycle = (365 * 400) + 100 - 4 + 1;
	59
	60	/* 28 year calendar cycle between 2010 and 2037 */
	61	static const int safe_years[28] = {
	62	2016, 2017, 2018, 2019,
	63	2020, 2021, 2022, 2023,
	64	2024, 2025, 2026, 2027,
	65	2028, 2029, 2030, 2031,
	66	2032, 2033, 2034, 2035,
	67	2036, 2037, 2010, 2011,
	68	2012, 2013, 2014, 2015
	69	};
	70
	71	static const int dow_year_start[28] = {
	72	5, 0, 1, 2, /* 2016 - 2019 */
	73	3, 5, 6, 0,
	74	1, 3, 4, 5,
	75	6, 1, 2, 3,
	76	4, 6, 0, 1,
	77	2, 4, 5, 6, /* 2036, 2037, 2010, 2011 */
	78	0, 2, 3, 4 /* 2012, 2013, 2014, 2015 */
	79	};
	80
9af24521	81	/* Let's assume people are going to be looking for dates in the future.
	82	Let's provide some cheats so you can skip ahead.
	83	This has a 4x speed boost when near 2008.
	84	*/
	85	/* Number of days since epoch on Jan 1st, 2008 GMT */
	86	#define CHEAT_DAYS (1199145600 / 24 / 60 / 60)
	87	#define CHEAT_YEARS 108
a272e669	88
	89	#define IS_LEAP(n) ((!(((n) + 1900) % 400) \|\| (!(((n) + 1900) % 4) && (((n) + 1900) % 100))) != 0)
	90	#define WRAP(a,b,m) ((a) = ((a) < 0 ) ? ((b)--, (a) + (m)) : (a))
	91
a64acb40	92	#define SHOULD_USE_SYSTEM_LOCALTIME(a) ( USE_SYSTEM_LOCALTIME && (a) <= SYSTEM_LOCALTIME_MAX )
	93	#define SHOULD_USE_SYSTEM_GMTIME(a) ( USE_SYSTEM_GMTIME && (a) <= SYSTEM_GMTIME_MAX )
	94
	95
9af24521	96	int _is_exception_century(Int64 year)
a272e669	97	{
	98	int is_exception = ((year % 100 == 0) && !(year % 400 == 0));
	99	/* printf("is_exception_century: %s\n", is_exception ? "yes" : "no"); */
	100
	101	return(is_exception);
	102	}
	103
9af24521	104
	105	/* timegm() is a GNU extension, so emulate it here if we need it */
	106	#ifdef HAS_TIMEGM
	107	# define TIMEGM(n) timegm(n);
	108	#else
	109	# define TIMEGM(n) _my_timegm(n);
a272e669	110	#endif
a272e669	111
9af24521	112	time_t _my_timegm(struct tm *date) {
	113	int days = 0;
	114	int seconds = 0;
	115	time_t time;
	116	int year;
a272e669	117
9af24521	118	if( date->tm_year > 70 ) {
	119	year = 70;
	120	while( year < date->tm_year ) {
	121	days += length_of_year[IS_LEAP(year)];
	122	year++;
a272e669	123	}
a272e669	124	}
9af24521	125	else if ( date->tm_year < 70 ) {
	126	year = 69;
	127	do {
	128	days -= length_of_year[IS_LEAP(year)];
	129	year--;
	130	} while( year >= date->tm_year );
	131	}
	132
	133	days += julian_days_by_month[IS_LEAP(date->tm_year)][date->tm_mon];
	134	days += date->tm_mday - 1;
	135
	136	seconds += date->tm_hour * 60 * 60;
	137	seconds += date->tm_min * 60;
	138	seconds += date->tm_sec;
	139
	140	time = (time_t)(days * 60 * 60 * 24) + seconds;
	141
	142	return(time);
	143	}
	144
	145
af9b2bf5	146	int _check_tm(struct tm *tm)
9af24521	147	{
9af24521	148	/* Don't forget leap seconds */
af9b2bf5	149	assert(tm->tm_sec >= 0);
9af24521	150	assert(tm->tm_sec <= 61);
9af24521	151
af9b2bf5	152	assert(tm->tm_min >= 0);
9af24521	153	assert(tm->tm_min <= 59);
	154
	155	assert(tm->tm_hour >= 0);
	156	assert(tm->tm_hour <= 23);
	157
	158	assert(tm->tm_mday >= 1);
af9b2bf5	159	assert(tm->tm_mday <= days_in_month[IS_LEAP(tm->tm_year)][tm->tm_mon]);
9af24521	160
	161	assert(tm->tm_mon >= 0);
	162	assert(tm->tm_mon <= 11);
	163
	164	assert(tm->tm_wday >= 0);
	165	assert(tm->tm_wday <= 6);
	166
	167	assert(tm->tm_yday >= 0);
af9b2bf5	168	assert(tm->tm_yday <= length_of_year[IS_LEAP(tm->tm_year)]);
9af24521	169
	170	#ifdef HAS_TM_TM_GMTOFF
	171	assert(tm->tm_gmtoff >= -24 * 60 * 60);
	172	assert(tm->tm_gmtoff <= 24 * 60 * 60);
	173	#endif
af9b2bf5	174
af9b2bf5	175	return 1;
a272e669	176	}
a64acb40	177
a272e669	178
	179	/* The exceptional centuries without leap years cause the cycle to
	180	shift by 16
	181	*/
9af24521	182	int _cycle_offset(Int64 year)
a272e669	183	{
9af24521	184	const Int64 start_year = 2000;
	185	Int64 year_diff = year - start_year - 1;
	186	Int64 exceptions = year_diff / 100;
a272e669	187	exceptions -= year_diff / 400;
	188
	189	assert( year >= 2001 );
	190
	191	/* printf("year: %d, exceptions: %d\n", year, exceptions); */
	192
	193	return exceptions * 16;
	194	}
	195
	196	/* For a given year after 2038, pick the latest possible matching
	197	year in the 28 year calendar cycle.
	198	*/
	199	#define SOLAR_CYCLE_LENGTH 28
9af24521	200	int _safe_year(Int64 year)
a272e669	201	{
a272e669	202	int safe_year;
9af24521	203	Int64 year_cycle = year + _cycle_offset(year);
a272e669	204
	205	/* Change non-leap xx00 years to an equivalent */
	206	if( _is_exception_century(year) )
	207	year_cycle += 11;
	208
	209	year_cycle %= SOLAR_CYCLE_LENGTH;
	210
	211	safe_year = safe_years[year_cycle];
	212
	213	assert(safe_year <= 2037 && safe_year >= 2010);
	214
	215	/*
	216	printf("year: %d, year_cycle: %d, safe_year: %d\n",
	217	year, year_cycle, safe_year);
	218	*/
	219
	220	return safe_year;
	221	}
	222
	223	struct tm gmtime64_r (const Time64_T in_time, struct tm *p)
	224	{
	225	int v_tm_sec, v_tm_min, v_tm_hour, v_tm_mon, v_tm_wday;
9af24521	226	Int64 v_tm_tday;
a272e669	227	int leap;
9af24521	228	Int64 m;
a272e669	229	Time64_T time = *in_time;
9af24521	230	Int64 year = 70;
a272e669	231
a64acb40	232	/* Use the system gmtime() if time_t is small enough */
	233	if( SHOULD_USE_SYSTEM_GMTIME(*in_time) ) {
	234	time_t safe_time = *in_time;
	235	localtime_r(&safe_time, p);
af9b2bf5	236	assert(_check_tm(p));
a64acb40	237	return p;
	238	}
	239
9af24521	240	#ifdef HAS_TM_TM_GMTOFF
a272e669	241	p->tm_gmtoff = 0;
	242	#endif
	243	p->tm_isdst = 0;
	244
9af24521	245	#ifdef HAS_TM_TM_ZONE
a272e669	246	p->tm_zone = "UTC";
	247	#endif
	248
	249	v_tm_sec = time % 60;
	250	time /= 60;
	251	v_tm_min = time % 60;
	252	time /= 60;
	253	v_tm_hour = time % 24;
	254	time /= 24;
	255	v_tm_tday = time;
	256	WRAP (v_tm_sec, v_tm_min, 60);
	257	WRAP (v_tm_min, v_tm_hour, 60);
	258	WRAP (v_tm_hour, v_tm_tday, 24);
	259	if ((v_tm_wday = (v_tm_tday + 4) % 7) < 0)
	260	v_tm_wday += 7;
	261	m = v_tm_tday;
a272e669	262
9af24521	263	if (m >= CHEAT_DAYS) {
	264	year = CHEAT_YEARS;
	265	m -= CHEAT_DAYS;
	266	}
	267
	268	if (m >= 0) {
a272e669	269	/* Gregorian cycles, this is huge optimization for distant times */
	270	while (m >= (Time64_T) days_in_gregorian_cycle) {
	271	m -= (Time64_T) days_in_gregorian_cycle;
	272	year += years_in_gregorian_cycle;
	273	}
	274
	275	/* Years */
	276	leap = IS_LEAP (year);
	277	while (m >= (Time64_T) length_of_year[leap]) {
	278	m -= (Time64_T) length_of_year[leap];
	279	year++;
	280	leap = IS_LEAP (year);
	281	}
	282
	283	/* Months */
	284	v_tm_mon = 0;
	285	while (m >= (Time64_T) days_in_month[leap][v_tm_mon]) {
	286	m -= (Time64_T) days_in_month[leap][v_tm_mon];
	287	v_tm_mon++;
	288	}
	289	} else {
9af24521	290	year--;
a272e669	291
	292	/* Gregorian cycles */
	293	while (m < (Time64_T) -days_in_gregorian_cycle) {
	294	m += (Time64_T) days_in_gregorian_cycle;
	295	year -= years_in_gregorian_cycle;
	296	}
	297
	298	/* Years */
	299	leap = IS_LEAP (year);
	300	while (m < (Time64_T) -length_of_year[leap]) {
	301	m += (Time64_T) length_of_year[leap];
	302	year--;
	303	leap = IS_LEAP (year);
	304	}
	305
	306	/* Months */
	307	v_tm_mon = 11;
	308	while (m < (Time64_T) -days_in_month[leap][v_tm_mon]) {
	309	m += (Time64_T) days_in_month[leap][v_tm_mon];
	310	v_tm_mon--;
	311	}
	312	m += (Time64_T) days_in_month[leap][v_tm_mon];
	313	}
	314
	315	p->tm_year = year;
	316	if( p->tm_year != year ) {
9af24521	317	#ifdef EOVERFLOW
a272e669	318	errno = EOVERFLOW;
9af24521	319	#endif
a272e669	320	return NULL;
	321	}
	322
	323	p->tm_mday = (int) m + 1;
	324	p->tm_yday = julian_days_by_month[leap][v_tm_mon] + m;
	325	p->tm_sec = v_tm_sec, p->tm_min = v_tm_min, p->tm_hour = v_tm_hour,
	326	p->tm_mon = v_tm_mon, p->tm_wday = v_tm_wday;
	327
af9b2bf5	328	assert(_check_tm(p));
a272e669	329
	330	return p;
	331	}
	332
	333
	334	struct tm localtime64_r (const Time64_T time, struct tm *local_tm)
	335	{
	336	time_t safe_time;
	337	struct tm gm_tm;
9af24521	338	Int64 orig_year;
a272e669	339	int month_diff;
a272e669	340
a64acb40	341	/* Use the system localtime() if time_t is small enough */
	342	if( SHOULD_USE_SYSTEM_LOCALTIME(*time) ) {
	343	safe_time = *time;
	344	localtime_r(&safe_time, local_tm);
af9b2bf5	345	assert(_check_tm(local_tm));
a64acb40	346	return local_tm;
	347	}
	348
a272e669	349	gmtime64_r(time, &gm_tm);
	350	orig_year = gm_tm.tm_year;
	351
	352	if (gm_tm.tm_year > (2037 - 1900))
	353	gm_tm.tm_year = _safe_year(gm_tm.tm_year + 1900) - 1900;
	354
9af24521	355	safe_time = TIMEGM(&gm_tm);
a272e669	356	localtime_r(&safe_time, local_tm);
	357
	358	local_tm->tm_year = orig_year;
	359	month_diff = local_tm->tm_mon - gm_tm.tm_mon;
	360
	361	/* When localtime is Dec 31st previous year and
	362	gmtime is Jan 1st next year.
	363	*/
	364	if( month_diff == 11 ) {
	365	local_tm->tm_year--;
	366	}
	367
	368	/* When localtime is Jan 1st, next year and
	369	gmtime is Dec 31st, previous year.
	370	*/
	371	if( month_diff == -11 ) {
	372	local_tm->tm_year++;
	373	}
	374
	375	/* GMT is Jan 1st, xx01 year, but localtime is still Dec 31st
	376	in a non-leap xx00. There is one point in the cycle
	377	we can't account for which the safe xx00 year is a leap
	378	year. So we need to correct for Dec 31st comming out as
	379	the 366th day of the year.
	380	*/
	381	if( !IS_LEAP(local_tm->tm_year) && local_tm->tm_yday == 365 )
	382	local_tm->tm_yday--;
	383
af9b2bf5	384	assert(_check_tm(local_tm));
a272e669	385
	386	return local_tm;
	387	}