lfg.c 2.6 KB

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102
  1. /*
  2. * Lagged Fibonacci PRNG
  3. * Copyright (c) 2008 Michael Niedermayer
  4. *
  5. * This file is part of FFmpeg.
  6. *
  7. * FFmpeg is free software; you can redistribute it and/or
  8. * modify it under the terms of the GNU Lesser General Public
  9. * License as published by the Free Software Foundation; either
  10. * version 2.1 of the License, or (at your option) any later version.
  11. *
  12. * FFmpeg is distributed in the hope that it will be useful,
  13. * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14. * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  15. * Lesser General Public License for more details.
  16. *
  17. * You should have received a copy of the GNU Lesser General Public
  18. * License along with FFmpeg; if not, write to the Free Software
  19. * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20. */
  21. #include <inttypes.h>
  22. #include <limits.h>
  23. #include <math.h>
  24. #include "lfg.h"
  25. #include "md5.h"
  26. #include "intreadwrite.h"
  27. #include "attributes.h"
  28. void av_cold av_lfg_init(AVLFG *c, unsigned int seed)
  29. {
  30. uint8_t tmp[16] = { 0 };
  31. int i;
  32. for (i = 8; i < 64; i += 4) {
  33. AV_WL32(tmp, seed);
  34. tmp[4] = i;
  35. av_md5_sum(tmp, tmp, 16);
  36. c->state[i ] = AV_RL32(tmp);
  37. c->state[i + 1] = AV_RL32(tmp + 4);
  38. c->state[i + 2] = AV_RL32(tmp + 8);
  39. c->state[i + 3] = AV_RL32(tmp + 12);
  40. }
  41. c->index = 0;
  42. }
  43. void av_bmg_get(AVLFG *lfg, double out[2])
  44. {
  45. double x1, x2, w;
  46. do {
  47. x1 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0;
  48. x2 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0;
  49. w = x1 * x1 + x2 * x2;
  50. } while (w >= 1.0);
  51. w = sqrt((-2.0 * log(w)) / w);
  52. out[0] = x1 * w;
  53. out[1] = x2 * w;
  54. }
  55. #ifdef TEST
  56. #include "log.h"
  57. #include "timer.h"
  58. int main(void)
  59. {
  60. int x = 0;
  61. int i, j;
  62. AVLFG state;
  63. av_lfg_init(&state, 0xdeadbeef);
  64. for (j = 0; j < 10000; j++) {
  65. START_TIMER
  66. for (i = 0; i < 624; i++) {
  67. //av_log(NULL, AV_LOG_ERROR, "%X\n", av_lfg_get(&state));
  68. x += av_lfg_get(&state);
  69. }
  70. STOP_TIMER("624 calls of av_lfg_get");
  71. }
  72. av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);
  73. /* BMG usage example */
  74. {
  75. double mean = 1000;
  76. double stddev = 53;
  77. av_lfg_init(&state, 42);
  78. for (i = 0; i < 1000; i += 2) {
  79. double bmg_out[2];
  80. av_bmg_get(&state, bmg_out);
  81. av_log(NULL, AV_LOG_INFO,
  82. "%f\n%f\n",
  83. bmg_out[0] * stddev + mean,
  84. bmg_out[1] * stddev + mean);
  85. }
  86. }
  87. return 0;
  88. }
  89. #endif