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54 lines
1.7 KiB
54 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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#ifndef FFMPEG_LFG_H |
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#define FFMPEG_LFG_H |
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typedef struct { |
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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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* Gets the next random unsigned 32bit number using a 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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c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63]; |
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return c->state[c->index++ & 63]; |
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} |
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/** |
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* Gets the next random unsigned 32bit number using a MLFG. |
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* |
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* Please also consider the 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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return c->state[c->index++ & 63] = 2*a*b+a+b; |
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} |
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#endif //FFMPEG_LFG_H
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