/*
** This file is in the public domain, so clarified as of
** 1996-06-05 by Arthur David Olson.
*/
/*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);
}