1/*
2** This file is in the public domain, so clarified as of
3** 1996-06-05 by Arthur David Olson.
4*/
5
6#include <sys/cdefs.h>
7#ifndef lint
8#ifndef NOID
9static char	elsieid[] __unused = "@(#)difftime.c	8.1";
10#endif /* !defined NOID */
11#endif /* !defined lint */
12__FBSDID("$FreeBSD$");
13
14/*LINTLIBRARY*/
15
16#include "namespace.h"
17#include "private.h"	/* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */
18#include "un-namespace.h"
19
20double
21difftime(time1, time0)
22const time_t	time1;
23const time_t	time0;
24{
25	/*
26	** If (sizeof (double) > sizeof (time_t)) simply convert and subtract
27	** (assuming that the larger type has more precision).
28	** This is the common real-world case circa 2004.
29	*/
30	if (sizeof (double) > sizeof (time_t))
31		return (double) time1 - (double) time0;
32	if (!TYPE_INTEGRAL(time_t)) {
33		/*
34		** time_t is floating.
35		*/
36		return time1 - time0;
37	}
38	if (!TYPE_SIGNED(time_t)) {
39		/*
40		** time_t is integral and unsigned.
41		** The difference of two unsigned values can't overflow
42		** if the minuend is greater than or equal to the subtrahend.
43		*/
44		if (time1 >= time0)
45			return time1 - time0;
46		else	return -((double) (time0 - time1));
47	}
48	/*
49	** time_t is integral and signed.
50	** Handle cases where both time1 and time0 have the same sign
51	** (meaning that their difference cannot overflow).
52	*/
53	if ((time1 < 0) == (time0 < 0))
54		return time1 - time0;
55	/*
56	** time1 and time0 have opposite signs.
57	** Punt if unsigned long is too narrow.
58	*/
59	if (sizeof (unsigned long) < sizeof (time_t))
60		return (double) time1 - (double) time0;
61	/*
62	** Stay calm...decent optimizers will eliminate the complexity below.
63	*/
64	if (time1 >= 0 /* && time0 < 0 */)
65		return (unsigned long) time1 +
66			(unsigned long) (-(time0 + 1)) + 1;
67	return -(double) ((unsigned long) time0 +
68		(unsigned long) (-(time1 + 1)) + 1);
69}
70