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mkgmtime.c
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mkgmtime.c
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/* mkgmtime.c - make time corresponding to a GMT timeval struct
$Id: mkgmtime.c,v 1.4 1998/05/15 21:52:24 neplokh Exp $
# Copyright 1998 by Carnegie Mellon University
#
# All Rights Reserved
#
# Permission to use, copy, modify, and distribute this software and its
# documentation for any purpose and without fee is hereby granted,
# provided that the above copyright notice appear in all copies and that
# both that copyright notice and this permission notice appear in
# supporting documentation, and that the name of CMU not be
# used in advertising or publicity pertaining to distribution of the
# software without specific, written prior permission.
#
# CMU DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING
# ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL
# CMU BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR
# ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
# WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
# ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
# SOFTWARE.
*
*/
/*
* Copyright (c) 1987, 1989, 1993
* The Regents of the University of California. All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Arthur David Olson of the National Cancer Institute.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
/*
** Adapted from code provided by Robert Elz, who writes:
** The "best" way to do mktime I think is based on an idea of Bob
** Kridle's (so its said...) from a long time ago. (mtxinu!kridle now).
** It does a binary search of the time_t space. Since time_t's are
** just 32 bits, its a max of 32 iterations (even at 64 bits it
** would still be very reasonable).
*/
#include <time.h>
#ifndef WRONG
#define WRONG (-1)
#endif /* !defined WRONG */
static int
tmcomp(atmp, btmp)
register const struct tm * const atmp;
register const struct tm * const btmp;
{
register int result;
if ((result = (atmp->tm_year - btmp->tm_year)) == 0 &&
(result = (atmp->tm_mon - btmp->tm_mon)) == 0 &&
(result = (atmp->tm_mday - btmp->tm_mday)) == 0 &&
(result = (atmp->tm_hour - btmp->tm_hour)) == 0 &&
(result = (atmp->tm_min - btmp->tm_min)) == 0)
result = atmp->tm_sec - btmp->tm_sec;
return result;
}
time_t
mkgmtime(tmp)
struct tm * const tmp;
{
register int dir;
register int bits;
register int saved_seconds;
time_t t;
struct tm yourtm, *mytm;
yourtm = *tmp;
saved_seconds = yourtm.tm_sec;
yourtm.tm_sec = 0;
/*
** Calculate the number of magnitude bits in a time_t
** (this works regardless of whether time_t is
** signed or unsigned, though lint complains if unsigned).
*/
for (bits = 0, t = 1; t > 0; ++bits, t <<= 1)
;
/*
** If time_t is signed, then 0 is the median value,
** if time_t is unsigned, then 1 << bits is median.
*/
t = (t < 0) ? 0 : ((time_t) 1 << bits);
for ( ; ; ) {
mytm = gmtime(&t);
dir = tmcomp(mytm, &yourtm);
if (dir != 0) {
if (bits-- < 0)
return WRONG;
if (bits < 0)
--t;
else if (dir > 0)
t -= (time_t) 1 << bits;
else t += (time_t) 1 << bits;
continue;
}
break;
}
t += saved_seconds;
return t;
}

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