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/* Fast pseudo-random bits based on clock_gettime.
Copyright (C) 2019 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
<http://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 timespec tv;
__clock_gettime (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
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