lfg.h 1.9 KB

1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162
  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 {
  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. c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63];
  36. return c->state[c->index++ & 63];
  37. }
  38. /**
  39. * Get the next random unsigned 32-bit number using a MLFG.
  40. *
  41. * Please also consider av_lfg_get() above, it is faster.
  42. */
  43. static inline unsigned int av_mlfg_get(AVLFG *c){
  44. unsigned int a= c->state[(c->index-55) & 63];
  45. unsigned int b= c->state[(c->index-24) & 63];
  46. return c->state[c->index++ & 63] = 2*a*b+a+b;
  47. }
  48. /**
  49. * Get the next two numbers generated by a Box-Muller Gaussian
  50. * generator using the random numbers issued by lfg.
  51. *
  52. * @param out array where the two generated numbers are placed
  53. */
  54. void av_bmg_get(AVLFG *lfg, double out[2]);
  55. #endif /* AVUTIL_LFG_H */