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87 lines
2.5 KiB
C
87 lines
2.5 KiB
C
/* Copyright (C) 1991-2024 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <errno.h>
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#include <time.h>
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#define SECS_PER_HOUR (60 * 60)
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#define SECS_PER_DAY (SECS_PER_HOUR * 24)
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/* Compute the `struct tm' representation of T,
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offset OFFSET seconds east of UTC,
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and store year, yday, mon, mday, wday, hour, min, sec into *TP.
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Return nonzero if successful. */
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int
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__offtime (__time64_t t, long int offset, struct tm *tp)
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{
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__time64_t days, rem, y;
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const unsigned short int *ip;
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days = t / SECS_PER_DAY;
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rem = t % SECS_PER_DAY;
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rem += offset;
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while (rem < 0)
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{
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rem += SECS_PER_DAY;
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--days;
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}
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while (rem >= SECS_PER_DAY)
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{
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rem -= SECS_PER_DAY;
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++days;
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}
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tp->tm_hour = rem / SECS_PER_HOUR;
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rem %= SECS_PER_HOUR;
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tp->tm_min = rem / 60;
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tp->tm_sec = rem % 60;
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/* January 1, 1970 was a Thursday. */
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tp->tm_wday = (4 + days) % 7;
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if (tp->tm_wday < 0)
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tp->tm_wday += 7;
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y = 1970;
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#define DIV(a, b) ((a) / (b) - ((a) % (b) < 0))
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#define LEAPS_THRU_END_OF(y) (DIV (y, 4) - DIV (y, 100) + DIV (y, 400))
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while (days < 0 || days >= (__isleap (y) ? 366 : 365))
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{
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/* Guess a corrected year, assuming 365 days per year. */
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__time64_t yg = y + days / 365 - (days % 365 < 0);
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/* Adjust DAYS and Y to match the guessed year. */
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days -= ((yg - y) * 365
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+ LEAPS_THRU_END_OF (yg - 1)
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- LEAPS_THRU_END_OF (y - 1));
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y = yg;
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}
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tp->tm_year = y - 1900;
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if (tp->tm_year != y - 1900)
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{
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/* The year cannot be represented due to overflow. */
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__set_errno (EOVERFLOW);
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return 0;
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}
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tp->tm_yday = days;
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ip = __mon_yday[__isleap(y)];
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for (y = 11; days < (long int) ip[y]; --y)
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continue;
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days -= ip[y];
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tp->tm_mon = y;
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tp->tm_mday = days + 1;
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return 1;
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}
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