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28f540f4 RM |
1 | /* Copyright (C) 1991, 1993 Free Software Foundation, Inc. |
2 | This file is part of the GNU C Library. | |
3 | ||
4 | The GNU C Library is free software; you can redistribute it and/or | |
5 | modify it under the terms of the GNU Library General Public License as | |
6 | published by the Free Software Foundation; either version 2 of the | |
7 | License, or (at your option) any later version. | |
8 | ||
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 | Library General Public License for more details. | |
13 | ||
14 | You should have received a copy of the GNU Library General Public | |
15 | License along with the GNU C Library; see the file COPYING.LIB. If | |
16 | not, write to the Free Software Foundation, Inc., 675 Mass Ave, | |
17 | Cambridge, MA 02139, USA. */ | |
18 | ||
19 | #include <ansidecl.h> | |
20 | #include <time.h> | |
21 | ||
28f540f4 | 22 | /* Defined in mktime.c. */ |
80fd7387 | 23 | extern CONST unsigned short int __mon_yday[2][13]; |
28f540f4 RM |
24 | |
25 | #define SECS_PER_HOUR (60 * 60) | |
26 | #define SECS_PER_DAY (SECS_PER_HOUR * 24) | |
27 | ||
c2216480 RM |
28 | /* Compute the `struct tm' representation of *T, |
29 | offset OFFSET seconds east of UTC, | |
30 | and store year, yday, mon, mday, wday, hour, min, sec into *TP. */ | |
31 | void | |
32 | DEFUN(__offtime, (t, offset, tp), | |
33 | CONST time_t *t AND long int offset AND struct tm *tp) | |
28f540f4 | 34 | { |
b20e47cb | 35 | register long int days, rem, y; |
28f540f4 RM |
36 | register CONST unsigned short int *ip; |
37 | ||
28f540f4 RM |
38 | days = *t / SECS_PER_DAY; |
39 | rem = *t % SECS_PER_DAY; | |
40 | rem += offset; | |
41 | while (rem < 0) | |
42 | { | |
43 | rem += SECS_PER_DAY; | |
44 | --days; | |
45 | } | |
46 | while (rem >= SECS_PER_DAY) | |
47 | { | |
48 | rem -= SECS_PER_DAY; | |
49 | ++days; | |
50 | } | |
c2216480 | 51 | tp->tm_hour = rem / SECS_PER_HOUR; |
28f540f4 | 52 | rem %= SECS_PER_HOUR; |
c2216480 RM |
53 | tp->tm_min = rem / 60; |
54 | tp->tm_sec = rem % 60; | |
28f540f4 | 55 | /* January 1, 1970 was a Thursday. */ |
c2216480 RM |
56 | tp->tm_wday = (4 + days) % 7; |
57 | if (tp->tm_wday < 0) | |
58 | tp->tm_wday += 7; | |
28f540f4 | 59 | y = 1970; |
b20e47cb RM |
60 | |
61 | # define LEAPS_THRU_END_OF(y) ((y) / 4 - (y) / 100 + (y) / 400) | |
62 | ||
63 | while (days < 0 || days >= (__isleap (y) ? 366 : 365)) | |
28f540f4 | 64 | { |
b20e47cb RM |
65 | /* Guess a corrected year, assuming 365 days per year. */ |
66 | int yg = y + days / 365 - (days % 365 < 0); | |
67 | ||
68 | /* Adjust DAYS and Y to match the guessed year. */ | |
69 | days -= ((yg - y) * 365 | |
70 | + LEAPS_THRU_END_OF (yg - 1) | |
71 | - LEAPS_THRU_END_OF (y - 1)); | |
72 | y = yg; | |
28f540f4 | 73 | } |
c2216480 RM |
74 | tp->tm_year = y - 1900; |
75 | tp->tm_yday = days; | |
80fd7387 RM |
76 | ip = __mon_yday[__isleap(y)]; |
77 | for (y = 11; days < ip[y]; --y) | |
78 | continue; | |
79 | days -= ip[y]; | |
c2216480 RM |
80 | tp->tm_mon = y; |
81 | tp->tm_mday = days + 1; | |
28f540f4 | 82 | } |