difftime
Olson, Arthur David (NIH/NCI)
olsona at dc37a.nci.nih.gov
Mon Nov 1 14:46:55 UTC 2004
Yet another iteration on difftime.c.
--ado
/*
** This file is in the public domain, so clarified as of
** 1996-06-05 by Arthur David Olson (arthur_david_olson at nih.gov).
*/
#ifndef lint
#ifndef NOID
static char elsieid[] = "%W%";
#endif /* !defined NOID */
#endif /* !defined lint */
/*LINTLIBRARY*/
#include "sys/types.h" /* for time_t */
#include "private.h" /* for TYPE_INTEGRAL and TYPE_SIGNED */
double
difftime(time1, time0)
const time_t time1;
const time_t time0;
{
/*
** If (sizeof (double) > sizeof (time_t)) simply convert and
subtract
** (assuming that the wider type has more precision).
** This is the common real-world case circa 2004.
*/
if (sizeof (double) > sizeof (time_t))
return (double) time1 - (double) time0;
if (!TYPE_INTEGRAL(time_t)) {
/*
** time_t is floating.
*/
return time1 - time0;
}
if (!TYPE_SIGNED(time_t)) {
/*
** time_t is integral and unsigned.
** The difference of two unsigned values can't overflow
** if the minuend is greater than or equal to the
subtrahend.
*/
if (time1 >= time0)
return time1 - time0;
else return -((double) (time0 - time1));
}
/*
** time_t is integral and signed.
** Handle cases where both time1 and time0 have the same sign
** (meaning that their difference cannot overflow).
*/
if (time1 >= 0 && time0 >= 0 || time1 < 0 && time0 < 0)
return time1 - time0;
/*
** time1 and time0 have opposite signs.
** Punt if unsigned long is too narrow.
*/
if (sizeof (unsigned long) < sizeof (time_t))
return (double) time1 - (double) time0;
/*
** Stay calm...decent optimizers will eliminate the complexity
below.
*/
if (time1 >= 0 /* && time0 < 0 */)
return (unsigned long) time1 +
(unsigned long) (-(time0 + 1)) + 1;
return -(double) ((unsigned long) time0 +
(unsigned long) (-(time1 + 1)) + 1);
}
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