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98 lines
2.5 KiB
98 lines
2.5 KiB
/* |
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* Lagged Fibonacci PRNG |
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* Copyright (c) 2008 Michael Niedermayer |
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* |
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* This file is part of FFmpeg. |
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* |
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* FFmpeg is free software; you can redistribute it and/or |
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* modify it under the terms of the GNU Lesser General Public |
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* License as published by the Free Software Foundation; either |
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* version 2.1 of the License, or (at your option) any later version. |
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* |
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* FFmpeg is distributed in the hope that it will be useful, |
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* but WITHOUT ANY WARRANTY; without even the implied warranty of |
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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* Lesser General Public License for more details. |
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* |
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* You should have received a copy of the GNU Lesser General Public |
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* License along with FFmpeg; if not, write to the Free Software |
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
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*/ |
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#include <inttypes.h> |
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#include "lfg.h" |
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#include "md5.h" |
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#include "intreadwrite.h" |
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#include "attributes.h" |
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void av_cold av_lfg_init(AVLFG *c, unsigned int seed){ |
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uint8_t tmp[16]={0}; |
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int i; |
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for(i=8; i<64; i+=4){ |
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AV_WL32(tmp, seed); tmp[4]=i; |
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av_md5_sum(tmp, tmp, 16); |
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c->state[i ]= AV_RL32(tmp); |
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c->state[i+1]= AV_RL32(tmp+4); |
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c->state[i+2]= AV_RL32(tmp+8); |
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c->state[i+3]= AV_RL32(tmp+12); |
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} |
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c->index=0; |
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} |
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void av_bmg_get(AVLFG *lfg, double out[2]) |
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{ |
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double x1, x2, w; |
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do { |
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x1 = 2.0/UINT_MAX*av_lfg_get(lfg) - 1.0; |
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x2 = 2.0/UINT_MAX*av_lfg_get(lfg) - 1.0; |
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w = x1*x1 + x2*x2; |
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} while (w >= 1.0); |
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w = sqrt((-2.0 * log(w)) / w); |
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out[0] = x1 * w; |
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out[1] = x2 * w; |
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} |
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#ifdef TEST |
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#include "log.h" |
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#include "timer.h" |
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int main(void) |
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{ |
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int x=0; |
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int i, j; |
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AVLFG state; |
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av_lfg_init(&state, 0xdeadbeef); |
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for (j = 0; j < 10000; j++) { |
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START_TIMER |
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for (i = 0; i < 624; i++) { |
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// av_log(NULL,AV_LOG_ERROR, "%X\n", av_lfg_get(&state)); |
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x+=av_lfg_get(&state); |
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} |
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STOP_TIMER("624 calls of av_lfg_get"); |
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} |
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av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x); |
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/* BMG usage example */ |
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{ |
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double mean = 1000; |
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double stddev = 53; |
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av_lfg_init(&state, 42); |
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for (i = 0; i < 1000; i += 2) { |
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double bmg_out[2]; |
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av_bmg_get(&state, bmg_out); |
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av_log(NULL, AV_LOG_INFO, |
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"%f\n%f\n", |
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bmg_out[0] * stddev + mean, |
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bmg_out[1] * stddev + mean); |
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} |
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} |
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return 0; |
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} |
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#endif
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