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/* Fast pseudo-random bits based on clock_gettime. Copyright (C) 2019-2021 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 |