lpc10/random.c

   1 /*
   2
   3  * Revision 1.2  1996/08/20  20:41:32  jaf
   4  * Removed all static local variables that were SAVE'd in the Fortran
   5  * code, and put them in struct lpc10_decoder_state that is passed as an
   6  * argument.
   7  *
   8  * Removed init function, since all initialization is now done in
   9  * init_lpc10_decoder_state().
  10  *
  11  * Revision 1.1  1996/08/19  22:30:49  jaf
  12  * Initial revision
  13  *
  14
  15 */
  16
  17 /*  -- translated by f2c (version 19951025).
  18    You must link the resulting object file with the libraries:
  19         -lf2c -lm   (in that order)
  20 */
  21
  22 #include "f2c.h"
  23
  24 extern integer random_(struct lpc10_decoder_state *st);
  25
  26 /* ********************************************************************** */
  27
  28 /*      RANDOM Version 49 */
  29
  30 /*
  31  * Revision 1.2  1996/08/20  20:41:32  jaf
  32  * Removed all static local variables that were SAVE'd in the Fortran
  33  * code, and put them in struct lpc10_decoder_state that is passed as an
  34  * argument.
  35  *
  36  * Removed init function, since all initialization is now done in
  37  * init_lpc10_decoder_state().
  38  *
  39  * Revision 1.1  1996/08/19  22:30:49  jaf
  40  * Initial revision
  41  * */
  42 /* Revision 1.3  1996/03/20  16:13:54  jaf */
  43 /* Rearranged comments a little bit, and added comments explaining that */
  44 /* even though there is local state here, there is no need to create an */
  45 /* ENTRY for reinitializing it. */
  46
  47 /* Revision 1.2  1996/03/14  22:25:29  jaf */
  48 /* Just rearranged the comments and local variable declarations a bit. */
  49
  50 /* Revision 1.1  1996/02/07 14:49:01  jaf */
  51 /* Initial revision */
  52
  53
  54 /* ********************************************************************* */
  55
  56 /*  Pseudo random number generator based on Knuth, Vol 2, p. 27. */
  57
  58 /* Function Return: */
  59 /*  RANDOM - Integer variable, uniformly distributed over -32768 to 32767 */
  60
  61 /* This subroutine maintains local state from one call to the next. */
  62 /* In the context of the LPC10 coder, there is no reason to reinitialize */
  63 /* this local state when switching between audio streams, because its */
  64 /* results are only used to generate noise for unvoiced frames. */
  65
  66 integer random_(struct lpc10_decoder_state *st)
  67 {
  68     /* Initialized data */
  69
  70     integer *j;
  71     integer *k;
  72     shortint *y;
  73
  74     /* System generated locals */
  75     integer ret_val;
  76
  77 /*      Parameters/constants */
  78 /*       Local state */
  79 /*   The following is a 16 bit 2's complement addition, */
  80 /*   with overflow checking disabled */
  81
  82     j = &(st->j);
  83     k = &(st->k);
  84     y = &(st->y[0]);
  85
  86     y[*k - 1] += y[*j - 1];
  87     ret_val = y[*k - 1];
  88     --(*k);
  89     if (*k <= 0) {
  90         *k = 5;
  91     }
  92     --(*j);
  93     if (*j <= 0) {
  94         *j = 5;
  95     }
  96     return ret_val;
  97 } /* random_ */
  98