1/* Computing deadlines for timeouts.
2 Copyright (C) 2017-2022 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library 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 GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <net-internal.h>
20
21#include <assert.h>
22#include <limits.h>
23#include <stdio.h>
24#include <stdint.h>
25#include <time.h>
26
27struct deadline_current_time
28__deadline_current_time (void)
29{
30 struct deadline_current_time result;
31 if (__clock_gettime64 (CLOCK_MONOTONIC, &result.current) != 0)
32 __clock_gettime64 (CLOCK_REALTIME, &result.current);
33 assert (result.current.tv_sec >= 0);
34 return result;
35}
36
37/* A special deadline value for which __deadline_is_infinite is
38 true. */
39static inline struct deadline
40infinite_deadline (void)
41{
42 return (struct deadline) { { -1, -1 } };
43}
44
45struct deadline
46__deadline_from_timeval (struct deadline_current_time current,
47 struct timeval tv)
48{
49 assert (__is_timeval_valid_timeout (tv));
50
51 /* Compute second-based deadline. Perform the addition in
52 uintmax_t, which is unsigned, to simply overflow detection. */
53 uintmax_t sec = current.current.tv_sec;
54 sec += tv.tv_sec;
55 if (sec < (uintmax_t) tv.tv_sec)
56 return infinite_deadline ();
57
58 /* Compute nanosecond deadline. */
59 int nsec = current.current.tv_nsec + tv.tv_usec * 1000;
60 if (nsec >= 1000 * 1000 * 1000)
61 {
62 /* Carry nanosecond overflow to seconds. */
63 nsec -= 1000 * 1000 * 1000;
64 if (sec + 1 < sec)
65 return infinite_deadline ();
66 ++sec;
67 }
68 /* This uses a GCC extension, otherwise these casts for detecting
69 overflow would not be defined. */
70 if ((time_t) sec < 0 || sec != (uintmax_t) (time_t) sec)
71 return infinite_deadline ();
72
73 return (struct deadline) { { sec, nsec } };
74}
75
76int
77__deadline_to_ms (struct deadline_current_time current,
78 struct deadline deadline)
79{
80 if (__deadline_is_infinite (deadline))
81 return INT_MAX;
82
83 if (current.current.tv_sec > deadline.absolute.tv_sec
84 || (current.current.tv_sec == deadline.absolute.tv_sec
85 && current.current.tv_nsec >= deadline.absolute.tv_nsec))
86 return 0;
87 time_t sec = deadline.absolute.tv_sec - current.current.tv_sec;
88 if (sec >= INT_MAX)
89 /* This value will overflow below. */
90 return INT_MAX;
91 int nsec = deadline.absolute.tv_nsec - current.current.tv_nsec;
92 if (nsec < 0)
93 {
94 /* Borrow from the seconds field. */
95 assert (sec > 0);
96 --sec;
97 nsec += 1000 * 1000 * 1000;
98 }
99
100 /* Prepare for rounding up to milliseconds. */
101 nsec += 999999;
102 if (nsec > 1000 * 1000 * 1000)
103 {
104 assert (sec < INT_MAX);
105 ++sec;
106 nsec -= 1000 * 1000 * 1000;
107 }
108
109 unsigned int msec = nsec / (1000 * 1000);
110 if (sec > INT_MAX / 1000)
111 return INT_MAX;
112 msec += sec * 1000;
113 if (msec > INT_MAX)
114 return INT_MAX;
115 return msec;
116}
117

source code of glibc/inet/deadline.c