47 lines
1.4 KiB
C
47 lines
1.4 KiB
C
#include "time_header.h"
|
|
|
|
double difftime(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).
|
|
*/
|
|
if (sizeof (double) > sizeof (time_t))
|
|
return (double) time1 - (double) time0;
|
|
|
|
if (!TYPE_SIGNED(time_t)) {
|
|
/*
|
|
** 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);
|
|
}
|
|
|
|
/*
|
|
** 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 uintmax_t is too narrow.
|
|
** This suffers from double rounding; attempt to lessen that
|
|
** by using long double temporaries.
|
|
*/
|
|
if (sizeof (uintmax_t) < sizeof (time_t))
|
|
return (long double) time1 - (long double) time0;
|
|
|
|
/*
|
|
** Stay calm...decent optimizers will eliminate the complexity below.
|
|
*/
|
|
if (time1 >= 0 /* && time0 < 0 */)
|
|
return (uintmax_t) time1 + (uintmax_t) (-1 - time0) + 1;
|
|
|
|
return -(double) ((uintmax_t) time0 + (uintmax_t) (-1 - time1) + 1);
|
|
}
|