lfg.h 2.0 KB

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  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. #ifndef AVUTIL_LFG_H
  22. #define AVUTIL_LFG_H
  23. typedef struct AVLFG {
  24. unsigned int state[64];
  25. int index;
  26. } AVLFG;
  27. void av_lfg_init(AVLFG *c, unsigned int seed);
  28. /**
  29. * Get the next random unsigned 32-bit number using an ALFG.
  30. *
  31. * Please also consider a simple LCG like state= state*1664525+1013904223,
  32. * it may be good enough and faster for your specific use case.
  33. */
  34. static inline unsigned int av_lfg_get(AVLFG *c){
  35. unsigned a = c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63];
  36. c->index += 1U;
  37. return a;
  38. }
  39. /**
  40. * Get the next random unsigned 32-bit number using a MLFG.
  41. *
  42. * Please also consider av_lfg_get() above, it is faster.
  43. */
  44. static inline unsigned int av_mlfg_get(AVLFG *c){
  45. unsigned int a= c->state[(c->index-55) & 63];
  46. unsigned int b= c->state[(c->index-24) & 63];
  47. a = c->state[c->index & 63] = 2*a*b+a+b;
  48. c->index += 1U;
  49. return a;
  50. }
  51. /**
  52. * Get the next two numbers generated by a Box-Muller Gaussian
  53. * generator using the random numbers issued by lfg.
  54. *
  55. * @param out array where the two generated numbers are placed
  56. */
  57. void av_bmg_get(AVLFG *lfg, double out[2]);
  58. #endif /* AVUTIL_LFG_H */