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80 lines
2.4 KiB
80 lines
2.4 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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#ifndef AVUTIL_LFG_H |
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#define AVUTIL_LFG_H |
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#include <stdint.h> |
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/** |
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* Context structure for the Lagged Fibonacci PRNG. |
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* The exact layout, types and content of this struct may change and should |
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* not be accessed directly. Only its sizeof() is guranteed to stay the same |
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* to allow easy instanciation. |
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*/ |
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typedef struct AVLFG { |
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unsigned int state[64]; |
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int index; |
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} AVLFG; |
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void av_lfg_init(AVLFG *c, unsigned int seed); |
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/** |
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* Seed the state of the ALFG using binary data. |
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* |
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* Return value: 0 on success, negative value (AVERROR) on failure. |
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*/ |
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int av_lfg_init_from_data(AVLFG *c, const uint8_t *data, unsigned int length); |
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/** |
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* Get the next random unsigned 32-bit number using an ALFG. |
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* |
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* Please also consider a simple LCG like state= state*1664525+1013904223, |
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* it may be good enough and faster for your specific use case. |
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*/ |
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static inline unsigned int av_lfg_get(AVLFG *c){ |
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unsigned a = c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63]; |
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c->index += 1U; |
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return a; |
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} |
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/** |
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* Get the next random unsigned 32-bit number using a MLFG. |
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* |
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* Please also consider av_lfg_get() above, it is faster. |
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*/ |
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static inline unsigned int av_mlfg_get(AVLFG *c){ |
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unsigned int a= c->state[(c->index-55) & 63]; |
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unsigned int b= c->state[(c->index-24) & 63]; |
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a = c->state[c->index & 63] = 2*a*b+a+b; |
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c->index += 1U; |
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return a; |
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} |
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/** |
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* Get the next two numbers generated by a Box-Muller Gaussian |
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* generator using the random numbers issued by lfg. |
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* |
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* @param out array where the two generated numbers are placed |
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*/ |
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void av_bmg_get(AVLFG *lfg, double out[2]); |
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#endif /* AVUTIL_LFG_H */
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