[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().

*/

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);
}


#ifdef NDEBUG
#define     CHECK_TM(a)
#else
#define     CHECK_TM(a)         _check_tm(a);

void _check_tm(struct tm *tm)
{
    int is_leap = IS_LEAP(tm->tm_year);

    /* 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_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]);

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


/* 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);
        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;

    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);
        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--;

    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
a272e669 MS	42	static const int days_in_month[2][12] = {
	43	{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
	44	{31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
	45	};
	46
	47	static const int julian_days_by_month[2][12] = {
	48	{0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334},
	49	{0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335},
	50	};
	51
	52	static const int length_of_year[2] = { 365, 366 };
	53
	54	/* Number of days in a 400 year Gregorian cycle */
	55	static const int years_in_gregorian_cycle = 400;
	56	static const int days_in_gregorian_cycle = (365 * 400) + 100 - 4 + 1;
	57
	58	/* 28 year calendar cycle between 2010 and 2037 */
	59	static const int safe_years[28] = {
	60	2016, 2017, 2018, 2019,
	61	2020, 2021, 2022, 2023,
	62	2024, 2025, 2026, 2027,
	63	2028, 2029, 2030, 2031,
	64	2032, 2033, 2034, 2035,
	65	2036, 2037, 2010, 2011,
	66	2012, 2013, 2014, 2015
	67	};
	68
	69	static const int dow_year_start[28] = {
	70	5, 0, 1, 2, /* 2016 - 2019 */
	71	3, 5, 6, 0,
	72	1, 3, 4, 5,
	73	6, 1, 2, 3,
	74	4, 6, 0, 1,
	75	2, 4, 5, 6, /* 2036, 2037, 2010, 2011 */
	76	0, 2, 3, 4 /* 2012, 2013, 2014, 2015 */
	77	};
	78
9af24521 MS	79	/* Let's assume people are going to be looking for dates in the future.
	80	Let's provide some cheats so you can skip ahead.
	81	This has a 4x speed boost when near 2008.
	82	*/
	83	/* Number of days since epoch on Jan 1st, 2008 GMT */
	84	#define CHEAT_DAYS (1199145600 / 24 / 60 / 60)
	85	#define CHEAT_YEARS 108
a272e669 MS	86
	87	#define IS_LEAP(n) ((!(((n) + 1900) % 400) \|\| (!(((n) + 1900) % 4) && (((n) + 1900) % 100))) != 0)
	88	#define WRAP(a,b,m) ((a) = ((a) < 0 ) ? ((b)--, (a) + (m)) : (a))
	89
a64acb40 MS	90	#define SHOULD_USE_SYSTEM_LOCALTIME(a) ( USE_SYSTEM_LOCALTIME && (a) <= SYSTEM_LOCALTIME_MAX )
	91	#define SHOULD_USE_SYSTEM_GMTIME(a) ( USE_SYSTEM_GMTIME && (a) <= SYSTEM_GMTIME_MAX )
	92
	93
9af24521	94	int _is_exception_century(Int64 year)
a272e669 MS	95	{
	96	int is_exception = ((year % 100 == 0) && !(year % 400 == 0));
	97	/* printf("is_exception_century: %s\n", is_exception ? "yes" : "no"); */
	98
	99	return(is_exception);
	100	}
	101
9af24521 MS	102
	103	/* timegm() is a GNU extension, so emulate it here if we need it */
	104	#ifdef HAS_TIMEGM
	105	# define TIMEGM(n) timegm(n);
	106	#else
	107	# define TIMEGM(n) _my_timegm(n);
a272e669 MS	108	#endif
a272e669 MS	109
9af24521 MS	110	time_t _my_timegm(struct tm *date) {
	111	int days = 0;
	112	int seconds = 0;
	113	time_t time;
	114	int year;
a272e669	115
9af24521 MS	116	if( date->tm_year > 70 ) {
	117	year = 70;
	118	while( year < date->tm_year ) {
	119	days += length_of_year[IS_LEAP(year)];
	120	year++;
a272e669 MS	121	}
a272e669 MS	122	}
9af24521 MS	123	else if ( date->tm_year < 70 ) {
	124	year = 69;
	125	do {
	126	days -= length_of_year[IS_LEAP(year)];
	127	year--;
	128	} while( year >= date->tm_year );
	129	}
	130
	131	days += julian_days_by_month[IS_LEAP(date->tm_year)][date->tm_mon];
	132	days += date->tm_mday - 1;
	133
	134	seconds += date->tm_hour * 60 * 60;
	135	seconds += date->tm_min * 60;
	136	seconds += date->tm_sec;
	137
	138	time = (time_t)(days * 60 * 60 * 24) + seconds;
	139
	140	return(time);
	141	}
	142
	143
a64acb40 MS	144	#ifdef NDEBUG
	145	#define CHECK_TM(a)
	146	#else
	147	#define CHECK_TM(a) _check_tm(a);
	148
9af24521 MS	149	void _check_tm(struct tm *tm)
	150	{
	151	int is_leap = IS_LEAP(tm->tm_year);
	152
	153	/* Don't forget leap seconds */
	154	assert(tm->tm_sec >= 0);
	155	assert(tm->tm_sec <= 61);
	156
	157	assert(tm->tm_min >= 0);
	158	assert(tm->tm_min <= 59);
	159
	160	assert(tm->tm_hour >= 0);
	161	assert(tm->tm_hour <= 23);
	162
	163	assert(tm->tm_mday >= 1);
	164	assert(tm->tm_mday <= days_in_month[is_leap][tm->tm_mon]);
	165
	166	assert(tm->tm_mon >= 0);
	167	assert(tm->tm_mon <= 11);
	168
	169	assert(tm->tm_wday >= 0);
	170	assert(tm->tm_wday <= 6);
	171
	172	assert(tm->tm_yday >= 0);
	173	assert(tm->tm_yday <= length_of_year[is_leap]);
	174
	175	#ifdef HAS_TM_TM_GMTOFF
	176	assert(tm->tm_gmtoff >= -24 * 60 * 60);
	177	assert(tm->tm_gmtoff <= 24 * 60 * 60);
	178	#endif
a272e669	179	}
a64acb40 MS	180	#endif
a64acb40 MS	181
a272e669 MS	182
	183	/* The exceptional centuries without leap years cause the cycle to
	184	shift by 16
	185	*/
9af24521	186	int _cycle_offset(Int64 year)
a272e669	187	{
9af24521 MS	188	const Int64 start_year = 2000;
	189	Int64 year_diff = year - start_year - 1;
	190	Int64 exceptions = year_diff / 100;
a272e669 MS	191	exceptions -= year_diff / 400;
	192
	193	assert( year >= 2001 );
	194
	195	/* printf("year: %d, exceptions: %d\n", year, exceptions); */
	196
	197	return exceptions * 16;
	198	}
	199
	200	/* For a given year after 2038, pick the latest possible matching
	201	year in the 28 year calendar cycle.
	202	*/
	203	#define SOLAR_CYCLE_LENGTH 28
9af24521	204	int _safe_year(Int64 year)
a272e669 MS	205	{
a272e669 MS	206	int safe_year;
9af24521	207	Int64 year_cycle = year + _cycle_offset(year);
a272e669 MS	208
	209	/* Change non-leap xx00 years to an equivalent */
	210	if( _is_exception_century(year) )
	211	year_cycle += 11;
	212
	213	year_cycle %= SOLAR_CYCLE_LENGTH;
	214
	215	safe_year = safe_years[year_cycle];
	216
	217	assert(safe_year <= 2037 && safe_year >= 2010);
	218
	219	/*
	220	printf("year: %d, year_cycle: %d, safe_year: %d\n",
	221	year, year_cycle, safe_year);
	222	*/
	223
	224	return safe_year;
	225	}
	226
	227	struct tm gmtime64_r (const Time64_T in_time, struct tm *p)
	228	{
	229	int v_tm_sec, v_tm_min, v_tm_hour, v_tm_mon, v_tm_wday;
9af24521	230	Int64 v_tm_tday;
a272e669	231	int leap;
9af24521	232	Int64 m;
a272e669	233	Time64_T time = *in_time;
9af24521	234	Int64 year = 70;
a272e669	235
a64acb40 MS	236	/* Use the system gmtime() if time_t is small enough */
	237	if( SHOULD_USE_SYSTEM_GMTIME(*in_time) ) {
	238	time_t safe_time = *in_time;
	239	localtime_r(&safe_time, p);
	240	CHECK_TM(p)
	241	return p;
	242	}
	243
9af24521	244	#ifdef HAS_TM_TM_GMTOFF
a272e669 MS	245	p->tm_gmtoff = 0;
	246	#endif
	247	p->tm_isdst = 0;
	248
9af24521	249	#ifdef HAS_TM_TM_ZONE
a272e669 MS	250	p->tm_zone = "UTC";
	251	#endif
	252
	253	v_tm_sec = time % 60;
	254	time /= 60;
	255	v_tm_min = time % 60;
	256	time /= 60;
	257	v_tm_hour = time % 24;
	258	time /= 24;
	259	v_tm_tday = time;
	260	WRAP (v_tm_sec, v_tm_min, 60);
	261	WRAP (v_tm_min, v_tm_hour, 60);
	262	WRAP (v_tm_hour, v_tm_tday, 24);
	263	if ((v_tm_wday = (v_tm_tday + 4) % 7) < 0)
	264	v_tm_wday += 7;
	265	m = v_tm_tday;
a272e669	266
9af24521 MS	267	if (m >= CHEAT_DAYS) {
	268	year = CHEAT_YEARS;
	269	m -= CHEAT_DAYS;
	270	}
	271
	272	if (m >= 0) {
a272e669 MS	273	/* Gregorian cycles, this is huge optimization for distant times */
	274	while (m >= (Time64_T) days_in_gregorian_cycle) {
	275	m -= (Time64_T) days_in_gregorian_cycle;
	276	year += years_in_gregorian_cycle;
	277	}
	278
	279	/* Years */
	280	leap = IS_LEAP (year);
	281	while (m >= (Time64_T) length_of_year[leap]) {
	282	m -= (Time64_T) length_of_year[leap];
	283	year++;
	284	leap = IS_LEAP (year);
	285	}
	286
	287	/* Months */
	288	v_tm_mon = 0;
	289	while (m >= (Time64_T) days_in_month[leap][v_tm_mon]) {
	290	m -= (Time64_T) days_in_month[leap][v_tm_mon];
	291	v_tm_mon++;
	292	}
	293	} else {
9af24521	294	year--;
a272e669 MS	295
	296	/* Gregorian cycles */
	297	while (m < (Time64_T) -days_in_gregorian_cycle) {
	298	m += (Time64_T) days_in_gregorian_cycle;
	299	year -= years_in_gregorian_cycle;
	300	}
	301
	302	/* Years */
	303	leap = IS_LEAP (year);
	304	while (m < (Time64_T) -length_of_year[leap]) {
	305	m += (Time64_T) length_of_year[leap];
	306	year--;
	307	leap = IS_LEAP (year);
	308	}
	309
	310	/* Months */
	311	v_tm_mon = 11;
	312	while (m < (Time64_T) -days_in_month[leap][v_tm_mon]) {
	313	m += (Time64_T) days_in_month[leap][v_tm_mon];
	314	v_tm_mon--;
	315	}
	316	m += (Time64_T) days_in_month[leap][v_tm_mon];
	317	}
	318
	319	p->tm_year = year;
	320	if( p->tm_year != year ) {
9af24521	321	#ifdef EOVERFLOW
a272e669	322	errno = EOVERFLOW;
9af24521	323	#endif
a272e669 MS	324	return NULL;
	325	}
	326
	327	p->tm_mday = (int) m + 1;
	328	p->tm_yday = julian_days_by_month[leap][v_tm_mon] + m;
	329	p->tm_sec = v_tm_sec, p->tm_min = v_tm_min, p->tm_hour = v_tm_hour,
	330	p->tm_mon = v_tm_mon, p->tm_wday = v_tm_wday;
	331
a64acb40	332	CHECK_TM(p)
a272e669 MS	333
	334	return p;
	335	}
	336
	337
	338	struct tm localtime64_r (const Time64_T time, struct tm *local_tm)
	339	{
	340	time_t safe_time;
	341	struct tm gm_tm;
9af24521	342	Int64 orig_year;
a272e669 MS	343	int month_diff;
a272e669 MS	344
a64acb40 MS	345	/* Use the system localtime() if time_t is small enough */
	346	if( SHOULD_USE_SYSTEM_LOCALTIME(*time) ) {
	347	safe_time = *time;
	348	localtime_r(&safe_time, local_tm);
	349	CHECK_TM(local_tm)
	350	return local_tm;
	351	}
	352
a272e669 MS	353	gmtime64_r(time, &gm_tm);
	354	orig_year = gm_tm.tm_year;
	355
	356	if (gm_tm.tm_year > (2037 - 1900))
	357	gm_tm.tm_year = _safe_year(gm_tm.tm_year + 1900) - 1900;
	358
9af24521	359	safe_time = TIMEGM(&gm_tm);
a272e669 MS	360	localtime_r(&safe_time, local_tm);
	361
	362	local_tm->tm_year = orig_year;
	363	month_diff = local_tm->tm_mon - gm_tm.tm_mon;
	364
	365	/* When localtime is Dec 31st previous year and
	366	gmtime is Jan 1st next year.
	367	*/
	368	if( month_diff == 11 ) {
	369	local_tm->tm_year--;
	370	}
	371
	372	/* When localtime is Jan 1st, next year and
	373	gmtime is Dec 31st, previous year.
	374	*/
	375	if( month_diff == -11 ) {
	376	local_tm->tm_year++;
	377	}
	378
	379	/* GMT is Jan 1st, xx01 year, but localtime is still Dec 31st
	380	in a non-leap xx00. There is one point in the cycle
	381	we can't account for which the safe xx00 year is a leap
	382	year. So we need to correct for Dec 31st comming out as
	383	the 366th day of the year.
	384	*/
	385	if( !IS_LEAP(local_tm->tm_year) && local_tm->tm_yday == 365 )
	386	local_tm->tm_yday--;
	387
a64acb40	388	CHECK_TM(local_tm)
a272e669 MS	389
	390	return local_tm;
	391	}