| Line | Branch | Exec | Source |
|---|---|---|---|
| 1 | /* | ||
| 2 | * Copyright (c) 2024 Michael Niedermayer <michael-ffmpeg@niedermayer.cc> | ||
| 3 | * | ||
| 4 | * This file is part of FFmpeg. | ||
| 5 | * | ||
| 6 | * FFmpeg is free software; you can redistribute it and/or | ||
| 7 | * modify it under the terms of the GNU Lesser General Public | ||
| 8 | * License as published by the Free Software Foundation; either | ||
| 9 | * version 2.1 of the License, or (at your option) any later version. | ||
| 10 | * | ||
| 11 | * FFmpeg is distributed in the hope that it will be useful, | ||
| 12 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| 13 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | ||
| 14 | * Lesser General Public License for more details. | ||
| 15 | * | ||
| 16 | * You should have received a copy of the GNU Lesser General Public | ||
| 17 | * License along with FFmpeg; if not, write to the Free Software | ||
| 18 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | ||
| 19 | * | ||
| 20 | */ | ||
| 21 | |||
| 22 | /** | ||
| 23 | * @file | ||
| 24 | * simple Pseudo Random Number Generator | ||
| 25 | * | ||
| 26 | * This is a implementation of SFC64, a 64-bit PRNG by Chris Doty-Humphrey. | ||
| 27 | * | ||
| 28 | * This Generator is much faster (0m1.872s) than 64bit KISS (0m3.823s) and PCG-XSH-RR-64/32 (0m2.700s) | ||
| 29 | * And passes testu01 and practrand test suits. | ||
| 30 | */ | ||
| 31 | |||
| 32 | #ifndef AVUTIL_SFC64_H | ||
| 33 | #define AVUTIL_SFC64_H | ||
| 34 | |||
| 35 | #include <inttypes.h> | ||
| 36 | |||
| 37 | typedef struct FFSFC64 { | ||
| 38 | uint64_t a,b,c,counter; | ||
| 39 | } FFSFC64; | ||
| 40 | |||
| 41 | 265561 | static inline uint64_t ff_sfc64_get(FFSFC64 *s) { | |
| 42 | 265561 | uint64_t tmp = s->a + s->b + s->counter++; | |
| 43 | 265561 | s->a = s->b ^ (s->b >> 11); | |
| 44 | 265561 | s->b = s->c + (s->c << 3); // This is a multiply by 9 | |
| 45 | 265561 | s->c = (s->c << 24 | s->c >> 40) + tmp; | |
| 46 | 265561 | return tmp; | |
| 47 | } | ||
| 48 | |||
| 49 | /** | ||
| 50 | * Return the previous random value, and step the generator backward. | ||
| 51 | * | ||
| 52 | * It is safe to take values before the first, but such values can be highly | ||
| 53 | * correlated to the seeds. | ||
| 54 | */ | ||
| 55 | static inline uint64_t ff_sfc64_reverse_get(FFSFC64 *s) { | ||
| 56 | uint64_t prev_c = s->b * 0x8E38E38E38E38E39; | ||
| 57 | uint64_t tmp = s->c - (prev_c << 24 | prev_c >> 40); | ||
| 58 | s->b = s->a ^ (s->a >> 11); | ||
| 59 | s->b ^= s->b >> 22; | ||
| 60 | s->b ^= s->b >> 44; | ||
| 61 | |||
| 62 | s->a = tmp - s->b - --s->counter; | ||
| 63 | s->c = prev_c; | ||
| 64 | |||
| 65 | return tmp; | ||
| 66 | } | ||
| 67 | |||
| 68 | /** | ||
| 69 | * Initialize sfc64 with up to 3 seeds. | ||
| 70 | * | ||
| 71 | * @param rounds number of rounds mixing up state during init. Generally 8-18, larger numbers will help with bad quality seeds. | ||
| 72 | * 12 is a good choice if all 3 seeds are equal | ||
| 73 | * | ||
| 74 | */ | ||
| 75 | 54 | static inline void ff_sfc64_init(FFSFC64 *s, uint64_t seeda, uint64_t seedb, uint64_t seedc, int rounds) { | |
| 76 | 54 | s->a = seeda; | |
| 77 | 54 | s->b = seedb; | |
| 78 | 54 | s->c = seedc; | |
| 79 | 54 | s->counter = 1; | |
| 80 |
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702 | while (rounds--) |
| 81 | 648 | ff_sfc64_get(s); | |
| 82 | 54 | } | |
| 83 | |||
| 84 | #endif // AVUTIL_SFC64_H | ||
| 85 |