## ffmpeg / libavutil / lfg.c @ 1fc81e73

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1 | 2754fe8b | Michael Niedermayer | ```
/*
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2 | ```
* Lagged Fibonacci PRNG
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3 | ```
* Copyright (c) 2008 Michael Niedermayer
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4 | ```
*
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5 | ```
* This file is part of FFmpeg.
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6 | ```
*
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7 | ```
* FFmpeg is free software; you can redistribute it and/or
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8 | ```
* modify it under the terms of the GNU Lesser General Public
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9 | ```
* License as published by the Free Software Foundation; either
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10 | ```
* version 2.1 of the License, or (at your option) any later version.
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11 | ```
*
``` |
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12 | ```
* FFmpeg is distributed in the hope that it will be useful,
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13 | ```
* but WITHOUT ANY WARRANTY; without even the implied warranty of
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14 | ```
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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15 | ```
* Lesser General Public License for more details.
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16 | ```
*
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17 | ```
* You should have received a copy of the GNU Lesser General Public
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18 | ```
* License along with FFmpeg; if not, write to the Free Software
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19 | ```
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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20 | ```
*/
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21 | |||

22 | #include <inttypes.h> |
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23 | f4d80ecb | Måns Rullgård | #include <limits.h> |

24 | #include <math.h> |
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25 | 2754fe8b | Michael Niedermayer | #include "lfg.h" |

26 | #include "md5.h" |
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27 | #include "intreadwrite.h" |
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28 | 2ed6f399 | Måns Rullgård | #include "attributes.h" |

29 | 2754fe8b | Michael Niedermayer | |

30 | void av_cold av_lfg_init(AVLFG *c, unsigned int seed){ |
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31 | uint8_t tmp[16]={0}; |
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32 | ```
int i;
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33 | |||

34 | for(i=8; i<64; i+=4){ |
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35 | ```
AV_WL32(tmp, seed); tmp[4]=i;
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36 | ```
av_md5_sum(tmp, tmp, 16);
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37 | c->state[i ]= AV_RL32(tmp); |
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38 | c->state[i+1]= AV_RL32(tmp+4); |
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39 | c->state[i+2]= AV_RL32(tmp+8); |
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40 | c->state[i+3]= AV_RL32(tmp+12); |
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41 | } |
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42 | ```
c->index=0;
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43 | } |
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44 | |||

45 | 3ba69a15 | Stefano Sabatini | void av_bmg_get(AVLFG *lfg, double out[2]) |

46 | { |
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47 | ```
double x1, x2, w;
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48 | |||

49 | ```
do {
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50 | x1 = 2.0/UINT_MAX*av_lfg_get(lfg) - 1.0; |
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51 | x2 = 2.0/UINT_MAX*av_lfg_get(lfg) - 1.0; |
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52 | w = x1*x1 + x2*x2; |
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53 | } while (w >= 1.0); |
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54 | |||

55 | w = sqrt((-2.0 * log(w)) / w); |
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56 | ```
out[0] = x1 * w;
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57 | ```
out[1] = x2 * w;
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58 | } |
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59 | |||

60 | 2754fe8b | Michael Niedermayer | ```
#ifdef TEST
``` |

61 | #include "log.h" |
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62 | 2ed6f399 | Måns Rullgård | #include "timer.h" |

63 | 2754fe8b | Michael Niedermayer | |

64 | int main(void) |
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65 | { |
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66 | int x=0; |
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67 | ```
int i, j;
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68 | AVLFG state; |
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69 | |||

70 | ```
av_lfg_init(&state, 0xdeadbeef);
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71 | for (j = 0; j < 10000; j++) { |
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72 | START_TIMER |
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73 | for (i = 0; i < 624; i++) { |
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74 | ```
// av_log(NULL,AV_LOG_ERROR, "%X\n", av_lfg_get(&state));
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75 | x+=av_lfg_get(&state); |
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76 | } |
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77 | 0e4cb6cb | Diego Biurrun | ```
STOP_TIMER("624 calls of av_lfg_get");
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78 | 2754fe8b | Michael Niedermayer | } |

79 | av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x); |
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80 | 3ba69a15 | Stefano Sabatini | |

81 | ```
/* BMG usage example */
``` |
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82 | { |
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83 | double mean = 1000; |
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84 | double stddev = 53; |
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85 | |||

86 | ```
av_lfg_init(&state, 42);
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87 | |||

88 | for (i = 0; i < 1000; i += 2) { |
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89 | double bmg_out[2]; |
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90 | av_bmg_get(&state, bmg_out); |
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91 | ```
av_log(NULL, AV_LOG_INFO,
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92 | ```
"%f\n%f\n",
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93 | ```
bmg_out[0] * stddev + mean,
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94 | ```
bmg_out[1] * stddev + mean);
``` |
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95 | } |
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96 | } |
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97 | |||

98 | 2754fe8b | Michael Niedermayer | return 0; |

99 | } |
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100 | `#endif` |