1 /* Copyright (C) 1991-2023 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <https://www.gnu.org/licenses/>. */
21 #define SECS_PER_HOUR (60 * 60)
22 #define SECS_PER_DAY (SECS_PER_HOUR * 24)
24 /* Compute the `struct tm' representation of T,
25 offset OFFSET seconds east of UTC,
26 and store year, yday, mon, mday, wday, hour, min, sec into *TP.
27 Return nonzero if successful. */
29 __offtime (__time64_t t, long int offset, struct tm *tp)
31 __time64_t days, rem, y;
32 const unsigned short int *ip;
34 days = t / SECS_PER_DAY;
35 rem = t % SECS_PER_DAY;
42 while (rem >= SECS_PER_DAY)
47 tp->tm_hour = rem / SECS_PER_HOUR;
49 tp->tm_min = rem / 60;
50 tp->tm_sec = rem % 60;
51 /* January 1, 1970 was a Thursday. */
52 tp->tm_wday = (4 + days) % 7;
57 #define DIV(a, b) ((a) / (b) - ((a) % (b) < 0))
58 #define LEAPS_THRU_END_OF(y) (DIV (y, 4) - DIV (y, 100) + DIV (y, 400))
60 while (days < 0 || days >= (__isleap (y) ? 366 : 365))
62 /* Guess a corrected year, assuming 365 days per year. */
63 __time64_t yg = y + days / 365 - (days % 365 < 0);
65 /* Adjust DAYS and Y to match the guessed year. */
66 days -= ((yg - y) * 365
67 + LEAPS_THRU_END_OF (yg - 1)
68 - LEAPS_THRU_END_OF (y - 1));
71 tp->tm_year = y - 1900;
72 if (tp->tm_year != y - 1900)
74 /* The year cannot be represented due to overflow. */
75 __set_errno (EOVERFLOW);
79 ip = __mon_yday[__isleap(y)];
80 for (y = 11; days < (long int) ip[y]; --y)
84 tp->tm_mday = days + 1;