mirror of https://git.videolan.org/git/ffmpeg.git
85 lines
2.5 KiB
C
85 lines
2.5 KiB
C
/*
|
|
* 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
|