Libav 0.7.1
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00001 /* 00002 * Lagged Fibonacci PRNG 00003 * Copyright (c) 2008 Michael Niedermayer 00004 * 00005 * This file is part of Libav. 00006 * 00007 * Libav is free software; you can redistribute it and/or 00008 * modify it under the terms of the GNU Lesser General Public 00009 * License as published by the Free Software Foundation; either 00010 * version 2.1 of the License, or (at your option) any later version. 00011 * 00012 * Libav is distributed in the hope that it will be useful, 00013 * but WITHOUT ANY WARRANTY; without even the implied warranty of 00014 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 00015 * Lesser General Public License for more details. 00016 * 00017 * You should have received a copy of the GNU Lesser General Public 00018 * License along with Libav; if not, write to the Free Software 00019 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 00020 */ 00021 00022 #include <inttypes.h> 00023 #include <limits.h> 00024 #include <math.h> 00025 #include "lfg.h" 00026 #include "md5.h" 00027 #include "intreadwrite.h" 00028 #include "attributes.h" 00029 00030 void av_cold av_lfg_init(AVLFG *c, unsigned int seed){ 00031 uint8_t tmp[16]={0}; 00032 int i; 00033 00034 for(i=8; i<64; i+=4){ 00035 AV_WL32(tmp, seed); tmp[4]=i; 00036 av_md5_sum(tmp, tmp, 16); 00037 c->state[i ]= AV_RL32(tmp); 00038 c->state[i+1]= AV_RL32(tmp+4); 00039 c->state[i+2]= AV_RL32(tmp+8); 00040 c->state[i+3]= AV_RL32(tmp+12); 00041 } 00042 c->index=0; 00043 } 00044 00045 void av_bmg_get(AVLFG *lfg, double out[2]) 00046 { 00047 double x1, x2, w; 00048 00049 do { 00050 x1 = 2.0/UINT_MAX*av_lfg_get(lfg) - 1.0; 00051 x2 = 2.0/UINT_MAX*av_lfg_get(lfg) - 1.0; 00052 w = x1*x1 + x2*x2; 00053 } while (w >= 1.0); 00054 00055 w = sqrt((-2.0 * log(w)) / w); 00056 out[0] = x1 * w; 00057 out[1] = x2 * w; 00058 } 00059 00060 #ifdef TEST 00061 #include "log.h" 00062 #include "timer.h" 00063 00064 int main(void) 00065 { 00066 int x=0; 00067 int i, j; 00068 AVLFG state; 00069 00070 av_lfg_init(&state, 0xdeadbeef); 00071 for (j = 0; j < 10000; j++) { 00072 START_TIMER 00073 for (i = 0; i < 624; i++) { 00074 // av_log(NULL,AV_LOG_ERROR, "%X\n", av_lfg_get(&state)); 00075 x+=av_lfg_get(&state); 00076 } 00077 STOP_TIMER("624 calls of av_lfg_get"); 00078 } 00079 av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x); 00080 00081 /* BMG usage example */ 00082 { 00083 double mean = 1000; 00084 double stddev = 53; 00085 00086 av_lfg_init(&state, 42); 00087 00088 for (i = 0; i < 1000; i += 2) { 00089 double bmg_out[2]; 00090 av_bmg_get(&state, bmg_out); 00091 av_log(NULL, AV_LOG_INFO, 00092 "%f\n%f\n", 00093 bmg_out[0] * stddev + mean, 00094 bmg_out[1] * stddev + mean); 00095 } 00096 } 00097 00098 return 0; 00099 } 00100 #endif