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60 lines
1.7 KiB
60 lines
1.7 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 <limits.h> |
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#include <math.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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av_cold void av_lfg_init(AVLFG *c, unsigned int seed) |
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{ |
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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); |
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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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