42 lines
1.5 KiB
C
42 lines
1.5 KiB
C
/* Fast pseudo-random bits based on clock_gettime.
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Copyright (C) 2019-2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#ifndef _RANDOM_BITS_H
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# define _RANDOM_BITS_H
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#include <time.h>
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#include <stdint.h>
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/* Provides fast pseudo-random bits through clock_gettime. It has unspecified
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starting time, nano-second accuracy, its randomness is significantly better
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than gettimeofday, and for mostly architectures it is implemented through
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vDSO instead of a syscall. Since the source is a system clock, the upper
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bits will have less entropy. */
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static inline uint32_t
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random_bits (void)
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{
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struct __timespec64 tv;
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__clock_gettime64 (CLOCK_MONOTONIC, &tv);
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/* Shuffle the lower bits to minimize the clock bias. */
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uint32_t ret = tv.tv_nsec ^ tv.tv_sec;
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ret ^= (ret << 24) | (ret >> 8);
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return ret;
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}
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#endif
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