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d3c70b9 Jul 27, 2015
59 lines (50 sloc) 1.37 KB
/*
** 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;
}
}
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