| /* |
| * Copyright (c) 2024 Michael Niedermayer <michael-ffmpeg@niedermayer.cc> |
| * |
| * This file is part of FFmpeg. |
| * |
| * FFmpeg 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. |
| * |
| * FFmpeg 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 FFmpeg; if not, write to the Free Software |
| * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
| * |
| */ |
| |
| /** |
| * @file |
| * simple Pseudo Random Number Generator |
| * |
| * This is a implementation of SFC64, a 64-bit PRNG by Chris Doty-Humphrey. |
| * |
| * This Generator is much faster (0m1.872s) than 64bit KISS (0m3.823s) and PCG-XSH-RR-64/32 (0m2.700s) |
| * And passes testu01 and practrand test suits. |
| */ |
| |
| #ifndef AVUTIL_SFC64_H |
| #define AVUTIL_SFC64_H |
| |
| #include <inttypes.h> |
| |
| typedef struct FFSFC64 { |
| uint64_t a,b,c,counter; |
| } FFSFC64; |
| |
| static inline uint64_t ff_sfc64_get(FFSFC64 *s) { |
| uint64_t tmp = s->a + s->b + s->counter++; |
| s->a = s->b ^ (s->b >> 11); |
| s->b = s->c + (s->c << 3); // This is a multiply by 9 |
| s->c = (s->c << 24 | s->c >> 40) + tmp; |
| return tmp; |
| } |
| |
| /** |
| * Return the previous random value, and step the generator backward. |
| * |
| * It is safe to take values before the first, but such values can be highly |
| * correlated to the seeds. |
| */ |
| static inline uint64_t ff_sfc64_reverse_get(FFSFC64 *s) { |
| uint64_t prev_c = s->b * 0x8E38E38E38E38E39; |
| uint64_t tmp = s->c - (prev_c << 24 | prev_c >> 40); |
| s->b = s->a ^ (s->a >> 11); |
| s->b ^= s->b >> 22; |
| s->b ^= s->b >> 44; |
| |
| s->a = tmp - s->b - --s->counter; |
| s->c = prev_c; |
| |
| return tmp; |
| } |
| |
| /** |
| * Initialize sfc64 with up to 3 seeds. |
| * |
| * @param rounds number of rounds mixing up state during init. Generally 8-18, larger numbers will help with bad quality seeds. |
| * 12 is a good choice if all 3 seeds are equal |
| * |
| */ |
| static inline void ff_sfc64_init(FFSFC64 *s, uint64_t seeda, uint64_t seedb, uint64_t seedc, int rounds) { |
| s->a = seeda; |
| s->b = seedb; |
| s->c = seedc; |
| s->counter = 1; |
| while (rounds--) |
| ff_sfc64_get(s); |
| } |
| |
| #endif // AVUTIL_SFC64_H |