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glibc/time/offtime.c
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/* Copyright (C) 1991-2016 Free Software Foundation, Inc. | |
This file is part of the GNU C Library. | |
The GNU C Library is free software; you can redistribute it and/or | |
modify it under the terms of the GNU Lesser General Public | |
License as published by the Free Software Foundation; either | |
version 2.1 of the License, or (at your option) any later version. | |
The GNU C Library is distributed in the hope that it will be useful, | |
but WITHOUT ANY WARRANTY; without even the implied warranty of | |
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
Lesser General Public License for more details. | |
You should have received a copy of the GNU Lesser General Public | |
License along with the GNU C Library; if not, see | |
<http://www.gnu.org/licenses/>. */ | |
#include <errno.h> | |
#include <time.h> | |
#define SECS_PER_HOUR (60 * 60) | |
#define SECS_PER_DAY (SECS_PER_HOUR * 24) | |
/* Compute the `struct tm' representation of *T, | |
offset OFFSET seconds east of UTC, | |
and store year, yday, mon, mday, wday, hour, min, sec into *TP. | |
Return nonzero if successful. */ | |
int | |
__offtime (const time_t *t, long int offset, struct tm *tp) | |
{ | |
time_t days, rem, y; | |
const unsigned short int *ip; | |
days = *t / SECS_PER_DAY; | |
rem = *t % SECS_PER_DAY; | |
rem += offset; | |
while (rem < 0) | |
{ | |
rem += SECS_PER_DAY; | |
--days; | |
} | |
while (rem >= SECS_PER_DAY) | |
{ | |
rem -= SECS_PER_DAY; | |
++days; | |
} | |
tp->tm_hour = rem / SECS_PER_HOUR; | |
rem %= SECS_PER_HOUR; | |
tp->tm_min = rem / 60; | |
tp->tm_sec = rem % 60; | |
/* January 1, 1970 was a Thursday. */ | |
tp->tm_wday = (4 + days) % 7; | |
if (tp->tm_wday < 0) | |
tp->tm_wday += 7; | |
y = 1970; | |
#define DIV(a, b) ((a) / (b) - ((a) % (b) < 0)) | |
#define LEAPS_THRU_END_OF(y) (DIV (y, 4) - DIV (y, 100) + DIV (y, 400)) | |
while (days < 0 || days >= (__isleap (y) ? 366 : 365)) | |
{ | |
/* Guess a corrected year, assuming 365 days per year. */ | |
time_t yg = y + days / 365 - (days % 365 < 0); | |
/* Adjust DAYS and Y to match the guessed year. */ | |
days -= ((yg - y) * 365 | |
+ LEAPS_THRU_END_OF (yg - 1) | |
- LEAPS_THRU_END_OF (y - 1)); | |
y = yg; | |
} | |
tp->tm_year = y - 1900; | |
if (tp->tm_year != y - 1900) | |
{ | |
/* The year cannot be represented due to overflow. */ | |
__set_errno (EOVERFLOW); | |
return 0; | |
} | |
tp->tm_yday = days; | |
ip = __mon_yday[__isleap(y)]; | |
for (y = 11; days < (long int) ip[y]; --y) | |
continue; | |
days -= ip[y]; | |
tp->tm_mon = y; | |
tp->tm_mday = days + 1; | |
return 1; | |
} |