(base_os): Linux is based on unix/sysv, not unix/sysv/sysv4.
[glibc.git] / time / offtime.c
bloba392a47e8988aac9fa8bfcdb4455f59d6c743751
1 /* Copyright (C) 1991, 1993 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 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.
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.
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. */
19 #include <ansidecl.h>
20 #include <time.h>
23 /* Defined in mktime.c. */
24 extern CONST unsigned short int __mon_lengths[2][12];
26 #define SECS_PER_HOUR (60 * 60)
27 #define SECS_PER_DAY (SECS_PER_HOUR * 24)
29 /* Returns the `struct tm' representation of *T,
30 offset OFFSET seconds east of UCT. */
31 struct tm *
32 DEFUN(__offtime, (t, offset), CONST time_t *t AND long int offset)
34 static struct tm tbuf;
35 register long int days, rem;
36 register int y;
37 register CONST unsigned short int *ip;
39 if (t == NULL)
40 return NULL;
42 days = *t / SECS_PER_DAY;
43 rem = *t % SECS_PER_DAY;
44 rem += offset;
45 while (rem < 0)
47 rem += SECS_PER_DAY;
48 --days;
50 while (rem >= SECS_PER_DAY)
52 rem -= SECS_PER_DAY;
53 ++days;
55 tbuf.tm_hour = rem / SECS_PER_HOUR;
56 rem %= SECS_PER_HOUR;
57 tbuf.tm_min = rem / 60;
58 tbuf.tm_sec = rem % 60;
59 /* January 1, 1970 was a Thursday. */
60 tbuf.tm_wday = (4 + days) % 7;
61 if (tbuf.tm_wday < 0)
62 tbuf.tm_wday += 7;
63 y = 1970;
64 while (days >= (rem = __isleap(y) ? 366 : 365))
66 ++y;
67 days -= rem;
69 while (days < 0)
71 --y;
72 days += __isleap(y) ? 366 : 365;
74 tbuf.tm_year = y - 1900;
75 tbuf.tm_yday = days;
76 ip = __mon_lengths[__isleap(y)];
77 for (y = 0; days >= ip[y]; ++y)
78 days -= ip[y];
79 tbuf.tm_mon = y;
80 tbuf.tm_mday = days + 1;
81 tbuf.tm_isdst = -1;
83 return &tbuf;