1/* Subtract two struct timespec values.
2 Copyright (C) 2011-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library and is also part of gnulib.
4 Patches to this file should be submitted to both projects.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <https://www.gnu.org/licenses/>. */
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
29struct timespec
30timespec_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 (struct timespec) { .tv_sec = rs, .tv_nsec = rns };
65}
66