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### Member "difftime.c" (1 Apr 2021, 1432 Bytes) of package /linux/misc/tzcode2022g.tar.gz:

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1 /* Return the difference between two timestamps. */
2
3 /*
4 ** This file is in the public domain, so clarified as of
5 ** 1996-06-05 by Arthur David Olson.
6 */
7
8 /*LINTLIBRARY*/
9
10 #include "private.h" /* for time_t and TYPE_SIGNED */
11
12 /* Return -X as a double. Using this avoids casting to 'double'. */
13 static double
14 dminus(double x)
15 {
16 return -x;
17 }
18
19 double
20 difftime(time_t time1, time_t time0)
21 {
22 /*
23 ** If double is large enough, simply convert and subtract
24 ** (assuming that the larger type has more precision).
25 */
26 if (sizeof(time_t) < sizeof(double)) {
27 double t1 = time1, t0 = time0;
28 return t1 - t0;
29 }
30
31 /*
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 (!TYPE_SIGNED(time_t))
36 return time0 <= time1 ? time1 - time0 : dminus(time0 - time1);
37
38 /* Use uintmax_t if wide enough. */
39 if (sizeof(time_t) <= sizeof(uintmax_t)) {
40 uintmax_t t1 = time1, t0 = time0;
41 return time0 <= time1 ? t1 - t0 : dminus(t0 - t1);
42 }
43
44 /*
45 ** Handle cases where both time1 and time0 have the same sign
46 ** (meaning that their difference cannot overflow).
47 */
48 if ((time1 < 0) == (time0 < 0))
49 return time1 - time0;
50
51 /*
52 ** The values have opposite signs and uintmax_t is too narrow.
53 ** This suffers from double rounding; attempt to lessen that
54 ** by using long double temporaries.
55 */
56 {
57 long double t1 = time1, t0 = time0;
58 return t1 - t0;
59 }
60 }