66 lines
1.7 KiB
C
66 lines
1.7 KiB
C
/*
|
|
** This file is in the public domain, so clarified as of
|
|
** 1996-06-05 by Arthur David Olson.
|
|
*/
|
|
|
|
#ifndef lint
|
|
#ifndef NOID
|
|
static char elsieid[] = "@(#)difftime.c 7.19";
|
|
#endif /* !defined NOID */
|
|
#endif /* !defined lint */
|
|
|
|
/*LINTLIBRARY*/
|
|
|
|
#include "private.h" /* for time_t, 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 larger 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))
|
|
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);
|
|
}
|