[perl5.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 &&              \
    (a) >= SYSTEM_LOCALTIME_MIN                 \
)
#define SHOULD_USE_SYSTEM_GMTIME(a)     (       \
    USE_SYSTEM_GMTIME           &&              \
    (a) <= SYSTEM_GMTIME_MAX    &&              \
    (a) >= SYSTEM_GMTIME_MIN                    \
)


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 MS	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 MS	42	#include "localtime64.h"
af9b2bf5 MS	43
a272e669 MS	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 MS	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 MS	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
7bda3dfc MS	92	#define SHOULD_USE_SYSTEM_LOCALTIME(a) ( \
	93	USE_SYSTEM_LOCALTIME && \
	94	(a) <= SYSTEM_LOCALTIME_MAX && \
	95	(a) >= SYSTEM_LOCALTIME_MIN \
	96	)
	97	#define SHOULD_USE_SYSTEM_GMTIME(a) ( \
	98	USE_SYSTEM_GMTIME && \
	99	(a) <= SYSTEM_GMTIME_MAX && \
	100	(a) >= SYSTEM_GMTIME_MIN \
	101	)
a64acb40 MS	102
a64acb40 MS	103
9af24521	104	int _is_exception_century(Int64 year)
a272e669 MS	105	{
	106	int is_exception = ((year % 100 == 0) && !(year % 400 == 0));
	107	/* printf("is_exception_century: %s\n", is_exception ? "yes" : "no"); */
	108
	109	return(is_exception);
	110	}
	111
9af24521 MS	112
	113	/* timegm() is a GNU extension, so emulate it here if we need it */
	114	#ifdef HAS_TIMEGM
	115	# define TIMEGM(n) timegm(n);
	116	#else
	117	# define TIMEGM(n) _my_timegm(n);
a272e669 MS	118	#endif
a272e669 MS	119
9af24521 MS	120	time_t _my_timegm(struct tm *date) {
	121	int days = 0;
	122	int seconds = 0;
	123	time_t time;
	124	int year;
a272e669	125
9af24521 MS	126	if( date->tm_year > 70 ) {
	127	year = 70;
	128	while( year < date->tm_year ) {
	129	days += length_of_year[IS_LEAP(year)];
	130	year++;
a272e669 MS	131	}
a272e669 MS	132	}
9af24521 MS	133	else if ( date->tm_year < 70 ) {
	134	year = 69;
	135	do {
	136	days -= length_of_year[IS_LEAP(year)];
	137	year--;
	138	} while( year >= date->tm_year );
	139	}
	140
	141	days += julian_days_by_month[IS_LEAP(date->tm_year)][date->tm_mon];
	142	days += date->tm_mday - 1;
	143
	144	seconds += date->tm_hour * 60 * 60;
	145	seconds += date->tm_min * 60;
	146	seconds += date->tm_sec;
	147
	148	time = (time_t)(days * 60 * 60 * 24) + seconds;
	149
	150	return(time);
	151	}
	152
	153
af9b2bf5	154	int _check_tm(struct tm *tm)
9af24521	155	{
9af24521	156	/* Don't forget leap seconds */
af9b2bf5	157	assert(tm->tm_sec >= 0);
9af24521 MS	158	assert(tm->tm_sec <= 61);
9af24521 MS	159
af9b2bf5	160	assert(tm->tm_min >= 0);
9af24521 MS	161	assert(tm->tm_min <= 59);
	162
	163	assert(tm->tm_hour >= 0);
	164	assert(tm->tm_hour <= 23);
	165
	166	assert(tm->tm_mday >= 1);
af9b2bf5	167	assert(tm->tm_mday <= days_in_month[IS_LEAP(tm->tm_year)][tm->tm_mon]);
9af24521 MS	168
	169	assert(tm->tm_mon >= 0);
	170	assert(tm->tm_mon <= 11);
	171
	172	assert(tm->tm_wday >= 0);
	173	assert(tm->tm_wday <= 6);
	174
	175	assert(tm->tm_yday >= 0);
af9b2bf5	176	assert(tm->tm_yday <= length_of_year[IS_LEAP(tm->tm_year)]);
9af24521 MS	177
	178	#ifdef HAS_TM_TM_GMTOFF
	179	assert(tm->tm_gmtoff >= -24 * 60 * 60);
	180	assert(tm->tm_gmtoff <= 24 * 60 * 60);
	181	#endif
af9b2bf5 MS	182
af9b2bf5 MS	183	return 1;
a272e669	184	}
a64acb40	185
a272e669 MS	186
	187	/* The exceptional centuries without leap years cause the cycle to
	188	shift by 16
	189	*/
9af24521	190	int _cycle_offset(Int64 year)
a272e669	191	{
9af24521 MS	192	const Int64 start_year = 2000;
	193	Int64 year_diff = year - start_year - 1;
	194	Int64 exceptions = year_diff / 100;
a272e669 MS	195	exceptions -= year_diff / 400;
	196
	197	assert( year >= 2001 );
	198
	199	/* printf("year: %d, exceptions: %d\n", year, exceptions); */
	200
	201	return exceptions * 16;
	202	}
	203
	204	/* For a given year after 2038, pick the latest possible matching
	205	year in the 28 year calendar cycle.
	206	*/
	207	#define SOLAR_CYCLE_LENGTH 28
9af24521	208	int _safe_year(Int64 year)
a272e669 MS	209	{
a272e669 MS	210	int safe_year;
9af24521	211	Int64 year_cycle = year + _cycle_offset(year);
a272e669 MS	212
	213	/* Change non-leap xx00 years to an equivalent */
	214	if( _is_exception_century(year) )
	215	year_cycle += 11;
	216
	217	year_cycle %= SOLAR_CYCLE_LENGTH;
	218
	219	safe_year = safe_years[year_cycle];
	220
	221	assert(safe_year <= 2037 && safe_year >= 2010);
	222
	223	/*
	224	printf("year: %d, year_cycle: %d, safe_year: %d\n",
	225	year, year_cycle, safe_year);
	226	*/
	227
	228	return safe_year;
	229	}
	230
	231	struct tm gmtime64_r (const Time64_T in_time, struct tm *p)
	232	{
	233	int v_tm_sec, v_tm_min, v_tm_hour, v_tm_mon, v_tm_wday;
9af24521	234	Int64 v_tm_tday;
a272e669	235	int leap;
9af24521	236	Int64 m;
a272e669	237	Time64_T time = *in_time;
9af24521	238	Int64 year = 70;
a272e669	239
a64acb40 MS	240	/* Use the system gmtime() if time_t is small enough */
	241	if( SHOULD_USE_SYSTEM_GMTIME(*in_time) ) {
	242	time_t safe_time = *in_time;
	243	localtime_r(&safe_time, p);
af9b2bf5	244	assert(_check_tm(p));
a64acb40 MS	245	return p;
	246	}
	247
9af24521	248	#ifdef HAS_TM_TM_GMTOFF
a272e669 MS	249	p->tm_gmtoff = 0;
	250	#endif
	251	p->tm_isdst = 0;
	252
9af24521	253	#ifdef HAS_TM_TM_ZONE
a272e669 MS	254	p->tm_zone = "UTC";
	255	#endif
	256
	257	v_tm_sec = time % 60;
	258	time /= 60;
	259	v_tm_min = time % 60;
	260	time /= 60;
	261	v_tm_hour = time % 24;
	262	time /= 24;
	263	v_tm_tday = time;
	264	WRAP (v_tm_sec, v_tm_min, 60);
	265	WRAP (v_tm_min, v_tm_hour, 60);
	266	WRAP (v_tm_hour, v_tm_tday, 24);
	267	if ((v_tm_wday = (v_tm_tday + 4) % 7) < 0)
	268	v_tm_wday += 7;
	269	m = v_tm_tday;
a272e669	270
9af24521 MS	271	if (m >= CHEAT_DAYS) {
	272	year = CHEAT_YEARS;
	273	m -= CHEAT_DAYS;
	274	}
	275
	276	if (m >= 0) {
a272e669 MS	277	/* Gregorian cycles, this is huge optimization for distant times */
	278	while (m >= (Time64_T) days_in_gregorian_cycle) {
	279	m -= (Time64_T) days_in_gregorian_cycle;
	280	year += years_in_gregorian_cycle;
	281	}
	282
	283	/* Years */
	284	leap = IS_LEAP (year);
	285	while (m >= (Time64_T) length_of_year[leap]) {
	286	m -= (Time64_T) length_of_year[leap];
	287	year++;
	288	leap = IS_LEAP (year);
	289	}
	290
	291	/* Months */
	292	v_tm_mon = 0;
	293	while (m >= (Time64_T) days_in_month[leap][v_tm_mon]) {
	294	m -= (Time64_T) days_in_month[leap][v_tm_mon];
	295	v_tm_mon++;
	296	}
	297	} else {
9af24521	298	year--;
a272e669 MS	299
	300	/* Gregorian cycles */
	301	while (m < (Time64_T) -days_in_gregorian_cycle) {
	302	m += (Time64_T) days_in_gregorian_cycle;
	303	year -= years_in_gregorian_cycle;
	304	}
	305
	306	/* Years */
	307	leap = IS_LEAP (year);
	308	while (m < (Time64_T) -length_of_year[leap]) {
	309	m += (Time64_T) length_of_year[leap];
	310	year--;
	311	leap = IS_LEAP (year);
	312	}
	313
	314	/* Months */
	315	v_tm_mon = 11;
	316	while (m < (Time64_T) -days_in_month[leap][v_tm_mon]) {
	317	m += (Time64_T) days_in_month[leap][v_tm_mon];
	318	v_tm_mon--;
	319	}
	320	m += (Time64_T) days_in_month[leap][v_tm_mon];
	321	}
	322
	323	p->tm_year = year;
	324	if( p->tm_year != year ) {
9af24521	325	#ifdef EOVERFLOW
a272e669	326	errno = EOVERFLOW;
9af24521	327	#endif
a272e669 MS	328	return NULL;
	329	}
	330
	331	p->tm_mday = (int) m + 1;
	332	p->tm_yday = julian_days_by_month[leap][v_tm_mon] + m;
	333	p->tm_sec = v_tm_sec, p->tm_min = v_tm_min, p->tm_hour = v_tm_hour,
	334	p->tm_mon = v_tm_mon, p->tm_wday = v_tm_wday;
	335
af9b2bf5	336	assert(_check_tm(p));
a272e669 MS	337
	338	return p;
	339	}
	340
	341
	342	struct tm localtime64_r (const Time64_T time, struct tm *local_tm)
	343	{
	344	time_t safe_time;
	345	struct tm gm_tm;
9af24521	346	Int64 orig_year;
a272e669 MS	347	int month_diff;
a272e669 MS	348
a64acb40 MS	349	/* Use the system localtime() if time_t is small enough */
	350	if( SHOULD_USE_SYSTEM_LOCALTIME(*time) ) {
	351	safe_time = *time;
	352	localtime_r(&safe_time, local_tm);
af9b2bf5	353	assert(_check_tm(local_tm));
a64acb40 MS	354	return local_tm;
	355	}
	356
a272e669 MS	357	gmtime64_r(time, &gm_tm);
	358	orig_year = gm_tm.tm_year;
	359
	360	if (gm_tm.tm_year > (2037 - 1900))
	361	gm_tm.tm_year = _safe_year(gm_tm.tm_year + 1900) - 1900;
	362
9af24521	363	safe_time = TIMEGM(&gm_tm);
a272e669 MS	364	localtime_r(&safe_time, local_tm);
	365
	366	local_tm->tm_year = orig_year;
	367	month_diff = local_tm->tm_mon - gm_tm.tm_mon;
	368
	369	/* When localtime is Dec 31st previous year and
	370	gmtime is Jan 1st next year.
	371	*/
	372	if( month_diff == 11 ) {
	373	local_tm->tm_year--;
	374	}
	375
	376	/* When localtime is Jan 1st, next year and
	377	gmtime is Dec 31st, previous year.
	378	*/
	379	if( month_diff == -11 ) {
	380	local_tm->tm_year++;
	381	}
	382
	383	/* GMT is Jan 1st, xx01 year, but localtime is still Dec 31st
	384	in a non-leap xx00. There is one point in the cycle
	385	we can't account for which the safe xx00 year is a leap
	386	year. So we need to correct for Dec 31st comming out as
	387	the 366th day of the year.
	388	*/
	389	if( !IS_LEAP(local_tm->tm_year) && local_tm->tm_yday == 365 )
	390	local_tm->tm_yday--;
	391
af9b2bf5	392	assert(_check_tm(local_tm));
a272e669 MS	393
	394	return local_tm;
	395	}