mirror of
https://github.com/mpv-player/mpv.git
synced 2025-12-22 10:57:08 +00:00
22f4ff44c5
removes awkward back-and-forth int -> double -> int conversion. the last step also broke uniformity, though it likely doesn't matter much in mpv's playlist shuffle context.
103 lines
2.7 KiB
C
103 lines
2.7 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 "common/common.h"
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#include "misc/mp_assert.h"
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#include "osdep/timer.h"
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#include "random.h"
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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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mp_rand_state mp_rand_seed(uint64_t seed)
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{
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mp_rand_state ret;
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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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if (av_random_bytes((void *)ret.v, sizeof(ret.v)) == 0) {
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return ret;
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}
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seed = mp_raw_time_ns();
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seed ^= (uintptr_t)&mp_rand_seed; // ASLR, hopefully
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seed += (uintptr_t)&ret; // stack position
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}
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ret.v[0] = seed;
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for (int i = 1; i < 4; i++)
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ret.v[i] = splitmix64(&seed);
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return ret;
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}
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uint64_t mp_rand_next(mp_rand_state *s)
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{
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uint64_t result, t;
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uint64_t *state = s->v;
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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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return result;
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}
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double mp_rand_next_double(mp_rand_state *s)
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{
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return (mp_rand_next(s) >> 11) * 0x1.0p-53;
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}
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// <https://web.archive.org/web/20250321082025/
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// https://www.pcg-random.org/posts/bounded-rands.html#bitmask-with-rejection-unbiased-apples-method>
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uint32_t mp_rand_in_range32(mp_rand_state *s, uint32_t min, uint32_t max)
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{
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mp_assert(min < max);
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uint32_t range = max - min;
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uint32_t mask = mp_round_next_power_of_2(range) - 1;
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uint32_t ret;
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do {
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ret = mp_rand_next(s) & mask;
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} while (ret >= range);
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return min + ret;
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}
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