2 ** This file is in the public domain, so clarified as of
3 ** 1996-06-05 by Arthur David Olson.
5 ** $FreeBSD: head/contrib/tzcode/stdtime/difftime.c 192625 2009-05-23 06:31:50Z edwin $
10 #include "private.h" /* for time_t and TYPE_SIGNED */
11 #include "un-namespace.h"
14 difftime(time_t time1, time_t time0)
17 ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract
18 ** (assuming that the larger type has more precision).
20 if (sizeof (double) > sizeof (time_t))
21 return (double) time1 - (double) time0;
22 if (!TYPE_SIGNED(time_t)) {
24 ** The difference of two unsigned values can't overflow
25 ** if the minuend is greater than or equal to the subtrahend.
29 else return -(double) (time0 - time1);
32 ** Handle cases where both time1 and time0 have the same sign
33 ** (meaning that their difference cannot overflow).
35 if ((time1 < 0) == (time0 < 0))
38 ** time1 and time0 have opposite signs.
39 ** Punt if uintmax_t is too narrow.
40 ** This suffers from double rounding; attempt to lessen that
41 ** by using long double temporaries.
43 if (sizeof (uintmax_t) < sizeof (time_t))
44 return (long double) time1 - (long double) time0;
46 ** Stay calm...decent optimizers will eliminate the complexity below.
48 if (time1 >= 0 /* && time0 < 0 */)
49 return (uintmax_t) time1 + (uintmax_t) (-1 - time0) + 1;
50 return -(double) ((uintmax_t) time0 + (uintmax_t) (-1 - time1) + 1);