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