From 2754fe8ba5519026d51af0edd2f0d05c6edfd84c Mon Sep 17 00:00:00 2001 From: Michael Niedermayer Date: Mon, 28 Jul 2008 15:35:04 +0000 Subject: Simple lagged fibonacci PRNG. 3.5 times faster than our mersene twister. 10 times less memory needed. (=less cache trashing) Originally committed as revision 14458 to svn://svn.ffmpeg.org/ffmpeg/trunk --- libavutil/lfg.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 64 insertions(+) create mode 100644 libavutil/lfg.c (limited to 'libavutil/lfg.c') diff --git a/libavutil/lfg.c b/libavutil/lfg.c new file mode 100644 index 0000000000..337ee9e41c --- /dev/null +++ b/libavutil/lfg.c @@ -0,0 +1,64 @@ +/* + * Lagged Fibonacci PRNG + * Copyright (c) 2008 Michael Niedermayer + * + * 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 + */ + +#include +#include "lfg.h" +#include "md5.h" +#include "intreadwrite.h" + +void av_cold av_lfg_init(AVLFG *c, unsigned int seed){ + uint8_t tmp[16]={0}; + int i; + + for(i=8; i<64; i+=4){ + AV_WL32(tmp, seed); tmp[4]=i; + av_md5_sum(tmp, tmp, 16); + c->state[i ]= AV_RL32(tmp); + c->state[i+1]= AV_RL32(tmp+4); + c->state[i+2]= AV_RL32(tmp+8); + c->state[i+3]= AV_RL32(tmp+12); + } + c->index=0; +} + +#ifdef TEST +#include "log.h" +#include "common.h" + +int main(void) +{ + int x=0; + int i, j; + AVLFG state; + + av_lfg_init(&state, 0xdeadbeef); + for (j = 0; j < 10000; j++) { + START_TIMER + for (i = 0; i < 624; i++) { +// av_log(NULL,AV_LOG_ERROR, "%X\n", av_lfg_get(&state)); + x+=av_lfg_get(&state); + } + STOP_TIMER("624 calls of av_random"); + } + av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x); + return 0; +} +#endif -- cgit v1.2.3