1 /* Subtract two struct timespec values.
2
3 Copyright (C) 2011-2023 Free Software Foundation, Inc.
4
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <https://www.gnu.org/licenses/>. */
17
18 /* Written by Paul Eggert. */
19
20 /* Return the difference between two timespec values A and B. On
21 overflow, return an extremal value. This assumes 0 <= tv_nsec <
22 TIMESPEC_HZ. */
23
24 #include <config.h>
25 #include "timespec.h"
26
27 #include <stdckdint.h>
28 #include "intprops.h"
29
30 struct timespec
31 timespec_sub (struct timespec a, struct timespec b)
32 {
33 time_t rs = a.tv_sec;
34 time_t bs = b.tv_sec;
35 int ns = a.tv_nsec - b.tv_nsec;
36 int rns = ns;
37
38 if (ns < 0)
39 {
40 rns = ns + TIMESPEC_HZ;
41 time_t bs1;
42 if (!ckd_add (&bs1, bs, 1))
43 bs = bs1;
44 else if (- TYPE_SIGNED (time_t) < rs)
45 rs--;
46 else
47 goto low_overflow;
48 }
49
50 if (ckd_sub (&rs, rs, bs))
51 {
52 if (0 < bs)
53 {
54 low_overflow:
55 rs = TYPE_MINIMUM (time_t);
56 rns = 0;
57 }
58 else
59 {
60 rs = TYPE_MAXIMUM (time_t);
61 rns = TIMESPEC_HZ - 1;
62 }
63 }
64
65 return make_timespec (rs, rns);
66 }