mirror of
https://github.com/mpv-player/mpv
synced 2024-12-27 09:32:40 +00:00
c365e2f7b1
When starting multiple processes of `mpv --shuffle` in parallel, sometimes the random seed happens to be identical, so files are played in the same random order. mp_rand_seed(0) now uses a random seed provided by libavutil, and only falls back to time in case of failure.
92 lines
2.3 KiB
C
92 lines
2.3 KiB
C
/*
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* Implementation of non-cryptographic pseudo-random number
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* generator algorithm known as xoshiro.
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*
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* This file is part of mpv.
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*
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* mpv 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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*
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* mpv 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
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* GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with mpv. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <stdint.h>
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#include <libavutil/random_seed.h>
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#include "osdep/threads.h"
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#include "osdep/timer.h"
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#include "random.h"
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static uint64_t state[4];
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static mp_static_mutex state_mutex = MP_STATIC_MUTEX_INITIALIZER;
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static inline uint64_t rotl_u64(const uint64_t x, const int k)
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{
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return (x << k) | (x >> (64 - k));
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}
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static inline uint64_t splitmix64(uint64_t *const x)
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{
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uint64_t z = (*x += UINT64_C(0x9e3779b97f4a7c15));
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z = (z ^ (z >> 30)) * UINT64_C(0xbf58476d1ce4e5b9);
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z = (z ^ (z >> 27)) * UINT64_C(0x94d049bb133111eb);
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return z ^ (z >> 31);
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}
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void mp_rand_seed(uint64_t seed)
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{
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#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
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seed = 42;
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#endif
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if (seed == 0) {
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uint8_t buf[sizeof(seed)];
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if (av_random_bytes(buf, sizeof(buf)) < 0) {
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seed = mp_raw_time_ns();
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} else {
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memcpy(&seed, buf, sizeof(seed));
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}
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}
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mp_mutex_lock(&state_mutex);
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state[0] = seed;
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for (int i = 1; i < 4; i++)
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state[i] = splitmix64(&seed);
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mp_mutex_unlock(&state_mutex);
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}
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uint64_t mp_rand_next(void)
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{
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uint64_t result, t;
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mp_mutex_lock(&state_mutex);
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result = rotl_u64(state[1] * 5, 7) * 9;
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t = state[1] << 17;
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state[2] ^= state[0];
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state[3] ^= state[1];
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state[1] ^= state[2];
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state[0] ^= state[3];
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state[2] ^= t;
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state[3] = rotl_u64(state[3], 45);
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mp_mutex_unlock(&state_mutex);
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return result;
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}
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double mp_rand_next_double(void)
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{
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return (mp_rand_next() >> 11) * 0x1.0p-53;
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}
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