compiler/alib/rangerand.c

   1 /*
   2     Copyright © 1995-2001, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc:
   6     Lang: english
   7 */
   8
   9 #include <exec/types.h>
  10
  11 ULONG RangeSeed;
  12
  13 /*****************************************************************************
  14
  15     NAME */
  16 #include <proto/alib.h>
  17
  18         ULONG RangeRand (
  19
  20 /*  SYNOPSIS */
  21         ULONG maxValue)
  22
  23 /*  FUNCTION
  24
  25     INPUTS
  26
  27     RESULT
  28
  29     NOTES
  30
  31     EXAMPLE
  32
  33     BUGS
  34
  35     SEE ALSO
  36
  37     INTERNALS
  38
  39     HISTORY
  40         06.12.96 digulla Created after original from libnix
  41
  42 ******************************************************************************/
  43 {
  44     ULONG a = RangeSeed;
  45     UWORD i = maxValue - 1;
  46
  47     do
  48     {
  49         ULONG b = a;
  50
  51         a <<= 1;
  52
  53         if ((LONG)b <= 0)
  54             a ^= 0x1d872b41;
  55
  56     } while ((i >>= 1));
  57
  58     RangeSeed = a;
  59
  60     if ((UWORD)maxValue)
  61         return (UWORD)((UWORD)a * (UWORD)maxValue >> 16);
  62
  63     return (UWORD)a;
  64 } /* RangeRand */
  65