]>
Commit | Line | Data |
---|---|---|
359653aa AZ |
1 | /* Fast pseudo-random bits based on clock_gettime. |
2 | Copyright (C) 2019 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 | |
5a82c748 | 17 | <https://www.gnu.org/licenses/>. */ |
359653aa AZ |
18 | |
19 | #ifndef _RANDOM_BITS_H | |
20 | # define _RANDOM_BITS_H | |
21 | ||
22 | #include <time.h> | |
23 | #include <stdint.h> | |
24 | ||
25 | /* Provides fast pseudo-random bits through clock_gettime. It has unspecified | |
26 | starting time, nano-second accuracy, its randomness is significantly better | |
27 | than gettimeofday, and for mostly architectures it is implemented through | |
28 | vDSO instead of a syscall. Since the source is a system clock, the upper | |
29 | bits will have less entropy. */ | |
30 | static inline uint32_t | |
31 | random_bits (void) | |
32 | { | |
33 | struct timespec tv; | |
34 | __clock_gettime (CLOCK_MONOTONIC, &tv); | |
35 | /* Shuffle the lower bits to minimize the clock bias. */ | |
36 | uint32_t ret = tv.tv_nsec ^ tv.tv_sec; | |
37 | ret ^= (ret << 24) | (ret >> 8); | |
38 | return ret; | |
39 | } | |
40 | ||
41 | #endif |