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authorRoland McGrath <roland@gnu.org>1995-02-18 01:27:10 +0000
committerRoland McGrath <roland@gnu.org>1995-02-18 01:27:10 +0000
commit28f540f45bbacd939bfd07f213bcad2bf730b1bf (patch)
tree15f07c4c43d635959c6afee96bde71fb1b3614ee /time/offtime.c
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initial import
Diffstat (limited to 'time/offtime.c')
-rw-r--r--time/offtime.c84
1 files changed, 84 insertions, 0 deletions
diff --git a/time/offtime.c b/time/offtime.c
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+++ b/time/offtime.c
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+/* Copyright (C) 1991, 1993 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 Library General Public License as
+published by the Free Software Foundation; either version 2 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
+Library General Public License for more details.
+
+You should have received a copy of the GNU Library General Public
+License along with the GNU C Library; see the file COPYING.LIB. If
+not, write to the Free Software Foundation, Inc., 675 Mass Ave,
+Cambridge, MA 02139, USA. */
+
+#include <ansidecl.h>
+#include <time.h>
+
+
+/* Defined in mktime.c. */
+extern CONST unsigned short int __mon_lengths[2][12];
+
+#define SECS_PER_HOUR (60 * 60)
+#define SECS_PER_DAY (SECS_PER_HOUR * 24)
+
+/* Returns the `struct tm' representation of *T,
+ offset OFFSET seconds east of UCT. */
+struct tm *
+DEFUN(__offtime, (t, offset), CONST time_t *t AND long int offset)
+{
+ static struct tm tbuf;
+ register long int days, rem;
+ register int y;
+ register CONST unsigned short int *ip;
+
+ if (t == NULL)
+ return NULL;
+
+ 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;
+ }
+ tbuf.tm_hour = rem / SECS_PER_HOUR;
+ rem %= SECS_PER_HOUR;
+ tbuf.tm_min = rem / 60;
+ tbuf.tm_sec = rem % 60;
+ /* January 1, 1970 was a Thursday. */
+ tbuf.tm_wday = (4 + days) % 7;
+ if (tbuf.tm_wday < 0)
+ tbuf.tm_wday += 7;
+ y = 1970;
+ while (days >= (rem = __isleap(y) ? 366 : 365))
+ {
+ ++y;
+ days -= rem;
+ }
+ while (days < 0)
+ {
+ --y;
+ days += __isleap(y) ? 366 : 365;
+ }
+ tbuf.tm_year = y - 1900;
+ tbuf.tm_yday = days;
+ ip = __mon_lengths[__isleap(y)];
+ for (y = 0; days >= ip[y]; ++y)
+ days -= ip[y];
+ tbuf.tm_mon = y;
+ tbuf.tm_mday = days + 1;
+ tbuf.tm_isdst = -1;
+
+ return &tbuf;
+}