1/*
2** This file is in the public domain, so clarified as of
3** 1996-06-05 by Arthur David Olson.
4*/
5
6/*LINTLIBRARY*/
7
8#include "private.h"	/* for time_t and TYPE_SIGNED */
9
10double ATTRIBUTE_CONST
11difftime(const time_t time1, const time_t time0)
12{
13	/*
14	** If (sizeof (double) > sizeof (time_t)) simply convert and subtract
15	** (assuming that the larger type has more precision).
16	*/
17	if (sizeof (double) > sizeof (time_t))
18		return (double) time1 - (double) time0;
19	if (!TYPE_SIGNED(time_t)) {
20		/*
21		** The difference of two unsigned values can't overflow
22		** if the minuend is greater than or equal to the subtrahend.
23		*/
24		if (time1 >= time0)
25			return            time1 - time0;
26		else	return -(double) (time0 - time1);
27	}
28	/*
29	** Handle cases where both time1 and time0 have the same sign
30	** (meaning that their difference cannot overflow).
31	*/
32	if ((time1 < 0) == (time0 < 0))
33		return time1 - time0;
34	/*
35	** time1 and time0 have opposite signs.
36	** Punt if uintmax_t is too narrow.
37	** This suffers from double rounding; attempt to lessen that
38	** by using long double temporaries.
39	*/
40	if (sizeof (uintmax_t) < sizeof (time_t))
41		return (long double) time1 - (long double) time0;
42	/*
43	** Stay calm...decent optimizers will eliminate the complexity below.
44	*/
45	if (time1 >= 0 /* && time0 < 0 */)
46		return    (uintmax_t) time1 + (uintmax_t) (-1 - time0) + 1;
47	return -(double) ((uintmax_t) time0 + (uintmax_t) (-1 - time1) + 1);
48}
49