1 /* Subtract two struct timespec values.
2
3 Copyright (C) 2011-2020 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 "intprops.h"
28
29 struct timespec
timespec_sub(struct timespec a,struct timespec b)30 timespec_sub (struct timespec a, struct timespec b)
31 {
32 time_t rs = a.tv_sec;
33 time_t bs = b.tv_sec;
34 int ns = a.tv_nsec - b.tv_nsec;
35 int rns = ns;
36
37 if (ns < 0)
38 {
39 rns = ns + TIMESPEC_HZ;
40 time_t bs1;
41 if (!INT_ADD_WRAPV (bs, 1, &bs1))
42 bs = bs1;
43 else if (- TYPE_SIGNED (time_t) < rs)
44 rs--;
45 else
46 goto low_overflow;
47 }
48
49 if (INT_SUBTRACT_WRAPV (rs, bs, &rs))
50 {
51 if (0 < bs)
52 {
53 low_overflow:
54 rs = TYPE_MINIMUM (time_t);
55 rns = 0;
56 }
57 else
58 {
59 rs = TYPE_MAXIMUM (time_t);
60 rns = TIMESPEC_HZ - 1;
61 }
62 }
63
64 return make_timespec (rs, rns);
65 }
66