1 /* $OpenBSD: difftime.c,v 1.9 2005/08/08 08:05:38 espie Exp $ */
2 /*
3 ** This file is in the public domain, so clarified as of
4 ** 1996-06-05 by Arthur David Olson.
5 */
6
7 /*LINTLIBRARY*/
8
9 #include "private.h" /* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */
10
11 __RCSID("$MirOS: src/lib/libc/time/difftime.c,v 1.2 2009/11/09 21:30:56 tg Exp $");
12
13 double
difftime(const time_t time1,const time_t time0)14 difftime(const time_t time1, const time_t time0)
15 {
16 /*
17 ** If (sizeof (double) > sizeof (time_t)) simply convert and subtract
18 ** (assuming that the larger type has more precision).
19 ** This is the common real-world case circa 2004.
20 */
21 if (sizeof (double) > sizeof (time_t))
22 return (double) time1 - (double) time0;
23 if (!TYPE_INTEGRAL(time_t)) {
24 /*
25 ** time_t is floating.
26 */
27 return time1 - time0;
28 }
29 if (!TYPE_SIGNED(time_t)) {
30 /*
31 ** time_t is integral and unsigned.
32 ** The difference of two unsigned values can't overflow
33 ** if the minuend is greater than or equal to the subtrahend.
34 */
35 if (time1 >= time0)
36 return time1 - time0;
37 else return -((double) (time0 - time1));
38 }
39 /*
40 ** time_t is integral and signed.
41 ** Handle cases where both time1 and time0 have the same sign
42 ** (meaning that their difference cannot overflow).
43 */
44 if ((time1 < 0) == (time0 < 0))
45 return time1 - time0;
46 /*
47 ** time1 and time0 have opposite signs.
48 ** Punt if unsigned long is too narrow.
49 */
50 if (sizeof (unsigned long) < sizeof (time_t))
51 return (double) time1 - (double) time0;
52 /*
53 ** Stay calm...decent optimizers will eliminate the complexity below.
54 */
55 if (time1 >= 0 /* && time0 < 0 */)
56 return (unsigned long) time1 +
57 (unsigned long) (-(time0 + 1)) + 1;
58 return -(double) ((unsigned long) time0 +
59 (unsigned long) (-(time1 + 1)) + 1);
60 }
61