mirror of
git://sourceware.org/git/glibc.git
synced 2024-12-09 04:11:27 +08:00
42 lines
1.5 KiB
C
42 lines
1.5 KiB
C
/* Fast pseudo-random bits based on clock_gettime.
|
|
Copyright (C) 2019-2024 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
|
|
The GNU C Library is free software; you can redistribute it and/or
|
|
modify it under the terms of the GNU Lesser General Public
|
|
License as published by the Free Software Foundation; either
|
|
version 2.1 of the License, or (at your option) any later version.
|
|
|
|
The GNU C Library is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
Lesser General Public License for more details.
|
|
|
|
You should have received a copy of the GNU Lesser General Public
|
|
License along with the GNU C Library; if not, see
|
|
<https://www.gnu.org/licenses/>. */
|
|
|
|
#ifndef _RANDOM_BITS_H
|
|
# define _RANDOM_BITS_H
|
|
|
|
#include <time.h>
|
|
#include <stdint.h>
|
|
|
|
/* Provides fast pseudo-random bits through clock_gettime. It has unspecified
|
|
starting time, nano-second accuracy, its randomness is significantly better
|
|
than gettimeofday, and for mostly architectures it is implemented through
|
|
vDSO instead of a syscall. Since the source is a system clock, the upper
|
|
bits will have less entropy. */
|
|
static inline uint32_t
|
|
random_bits (void)
|
|
{
|
|
struct __timespec64 tv;
|
|
__clock_gettime64 (CLOCK_MONOTONIC, &tv);
|
|
/* Shuffle the lower bits to minimize the clock bias. */
|
|
uint32_t ret = tv.tv_nsec ^ tv.tv_sec;
|
|
ret ^= (ret << 24) | (ret >> 8);
|
|
return ret;
|
|
}
|
|
|
|
#endif
|