1 | /* Fast pseudo-random bits based on clock_gettime. |
2 | Copyright (C) 2019-2024 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 | #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 __timespec64 tv; |
34 | __clock_gettime64 (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 |
42 | |