drand48-iter.c 1.8 KB

12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758
  1. /* Copyright (C) 1995, 1996, 2001 Free Software Foundation, Inc.
  2. This file is part of the GNU C Library.
  3. Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu <mailto:drepper@gnu.ai.mit.edu>>, August 1995.
  4. The GNU C Library is free software; you can redistribute it and/or
  5. modify it under the terms of the GNU Lesser General Public
  6. License as published by the Free Software Foundation; either
  7. version 2.1 of the License, or (at your option) any later version.
  8. The GNU C Library is distributed in the hope that it will be useful,
  9. but WITHOUT ANY WARRANTY; without even the implied warranty of
  10. MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  11. Lesser General Public License for more details.
  12. You should have received a copy of the GNU Lesser General Public
  13. License along with the GNU C Library; if not, write to the Free
  14. Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  15. 02111-1307 USA. */
  16. #include <errno.h>
  17. #include <stdlib.h>
  18. #include <limits.h>
  19. #include <stdint.h>
  20. #include <sys/types.h>
  21. /* Global state for non-reentrant functions. */
  22. struct drand48_data __libc_drand48_data;
  23. int
  24. __drand48_iterate (unsigned short int xsubi[3], struct drand48_data *buffer)
  25. {
  26. uint64_t X;
  27. uint64_t result;
  28. /* Initialize buffer, if not yet done. */
  29. if (unlikely(!buffer->__init))
  30. {
  31. buffer->__a = 0x5deece66dull;
  32. buffer->__c = 0xb;
  33. buffer->__init = 1;
  34. }
  35. /* Do the real work. We choose a data type which contains at least
  36. 48 bits. Because we compute the modulus it does not care how
  37. many bits really are computed. */
  38. X = (uint64_t) xsubi[2] << 32 | (uint32_t) xsubi[1] << 16 | xsubi[0];
  39. result = X * buffer->__a + buffer->__c;
  40. xsubi[0] = result & 0xffff;
  41. xsubi[1] = (result >> 16) & 0xffff;
  42. xsubi[2] = (result >> 32) & 0xffff;
  43. return 0;
  44. }