59 lines
1.4 KiB
C
59 lines
1.4 KiB
C
/*
|
|
** 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 and TYPE_SIGNED */
|
|
|
|
/* Return -X as a double. Using this avoids casting to 'double'. */
|
|
static double
|
|
dminus(double x)
|
|
{
|
|
return -x;
|
|
}
|
|
|
|
double ATTRIBUTE_CONST
|
|
difftime(time_t time1, time_t time0)
|
|
{
|
|
/*
|
|
** If double is large enough, simply convert and subtract
|
|
** (assuming that the larger type has more precision).
|
|
*/
|
|
if (sizeof (time_t) < sizeof (double)) {
|
|
double t1 = time1, t0 = time0;
|
|
return t1 - t0;
|
|
}
|
|
|
|
/*
|
|
** The difference of two unsigned values can't overflow
|
|
** if the minuend is greater than or equal to the subtrahend.
|
|
*/
|
|
if (!TYPE_SIGNED(time_t))
|
|
return time0 <= time1 ? time1 - time0 : dminus(time0 - time1);
|
|
|
|
/* Use uintmax_t if wide enough. */
|
|
if (sizeof (time_t) <= sizeof (uintmax_t)) {
|
|
uintmax_t t1 = time1, t0 = time0;
|
|
return time0 <= time1 ? t1 - t0 : dminus(t0 - t1);
|
|
}
|
|
|
|
/*
|
|
** 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;
|
|
|
|
/*
|
|
** The values have opposite signs and uintmax_t is too narrow.
|
|
** This suffers from double rounding; attempt to lessen that
|
|
** by using long double temporaries.
|
|
*/
|
|
{
|
|
long double t1 = time1, t0 = time0;
|
|
return t1 - t0;
|
|
}
|
|
}
|