random.c

   1 #include <stdio.h>
   2
   3 #include "random.h"
   4
   5
   6 /* Simple Park-Miller */
   7
   8 static __thread unsigned long pmseed = 29264;
   9
  10 void
  11 fast_srandom(unsigned long seed_)
  12 {
  13         pmseed = seed_;
  14 }
  15
  16 unsigned long
  17 fast_getseed(void)
  18 {
  19         return pmseed;
  20 }
  21
  22 uint16_t
  23 fast_random(unsigned int max)
  24 {
  25         unsigned long hi, lo;
  26         lo = 16807 * (pmseed & 0xffff);
  27         hi = 16807 * (pmseed >> 16);
  28         lo += (hi & 0x7fff) << 16;
  29         lo += hi >> 15;
  30         pmseed = (lo & 0x7fffffff) + (lo >> 31);
  31         return ((pmseed & 0xffff) * max) >> 16;
  32 }
  33
  34 float
  35 fast_frandom(void)
  36 {
  37         /* Construct (1,2) IEEE float from our random integer */
  38         /* http://rgba.org/articles/sfrand/sfrand.htm */
  39         union { unsigned long ul; float f; } p;
  40         p.ul = (((pmseed *= 16807) & 0x007fffff) - 1) | 0x3f800000;
  41         return p.f - 1.0f;
  42 }