gsl_rng__coveyou.c 2.2 KB

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  1. /* rng/coveyou.c
  2. *
  3. * This program is free software; you can redistribute it and/or modify
  4. * it under the terms of the GNU General Public License as published by
  5. * the Free Software Foundation; either version 3 of the License, or (at
  6. * your option) any later version.
  7. *
  8. * This program is distributed in the hope that it will be useful, but
  9. * WITHOUT ANY WARRANTY; without even the implied warranty of
  10. * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  11. * General Public License for more details.
  12. *
  13. * You should have received a copy of the GNU General Public License
  14. * along with this program; if not, write to the Free Software
  15. * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  16. */
  17. /*
  18. * This generator is taken from
  19. *
  20. * Donald E. Knuth
  21. * The Art of Computer Programming
  22. * Volume 2
  23. * Third Edition
  24. * Addison-Wesley
  25. * Section 3.2.2
  26. *
  27. * This implementation copyright (C) 2001 Carlo Perassi
  28. * and (C) 2003 Heiko Bauke.
  29. * Carlo Perassi reorganized the code to use the rng framework of GSL.
  30. */
  31. #include "gsl__config.h"
  32. #include <stdlib.h>
  33. #include "gsl_rng.h"
  34. #define MM 0xffffffffUL /* 2 ^ 32 - 1 */
  35. static inline unsigned long int ran_get (void *vstate);
  36. static double ran_get_double (void *vstate);
  37. static void ran_set (void *state, unsigned long int s);
  38. typedef struct
  39. {
  40. unsigned long int x;
  41. }
  42. ran_state_t;
  43. static inline unsigned long int
  44. ran_get (void *vstate)
  45. {
  46. ran_state_t *state = (ran_state_t *) vstate;
  47. state->x = (state->x * (state->x + 1)) & MM;
  48. return state->x;
  49. }
  50. static double
  51. ran_get_double (void *vstate)
  52. {
  53. ran_state_t *state = (ran_state_t *) vstate;
  54. return ran_get (state) / 4294967296.0;
  55. }
  56. static void
  57. ran_set (void *vstate, unsigned long int s)
  58. {
  59. ran_state_t *state = (ran_state_t *) vstate;
  60. unsigned long int diff = ((s % 4UL) - 2UL) % MM;
  61. if (diff)
  62. state->x = (s - diff) & MM;
  63. else
  64. state->x = s & MM;
  65. return;
  66. }
  67. static const gsl_rng_type ran_type = {
  68. "coveyou", /* name */
  69. MM-1, /* RAND_MAX */
  70. 2, /* RAND_MIN */
  71. sizeof (ran_state_t),
  72. &ran_set,
  73. &ran_get,
  74. &ran_get_double
  75. };
  76. const gsl_rng_type *gsl_rng_coveyou = &ran_type;