random.c

   1 #include <stdio.h>
   2
   3 #include "random.h"
   4
   5
   6 /* Simple Park-Miller for floating point; LCG as used in glibc and other places */
   7
   8 #ifndef NO_THREAD_LOCAL
   9
  10 static __thread unsigned long pmseed = 29264;
  11
  12 void
  13 fast_srandom(unsigned long seed_)
  14 {
  15         pmseed = seed_;
  16 }
  17
  18 unsigned long
  19 fast_getseed(void)
  20 {
  21         return pmseed;
  22 }
  23
  24 uint16_t
  25 fast_random(unsigned int max)
  26 {
  27         pmseed = ((pmseed * 1103515245) + 12345) & 0x7fffffff;
  28         return ((pmseed & 0xffff) * max) >> 16;
  29 }
  30
  31 float
  32 fast_frandom(void)
  33 {
  34         /* Construct (1,2) IEEE floating_t from our random integer */
  35         /* http://rgba.org/articles/sfrand/sfrand.htm */
  36         union { unsigned long ul; floating_t f; } p;
  37         p.ul = (((pmseed *= 16807) & 0x007fffff) - 1) | 0x3f800000;
  38         return p.f - 1.0f;
  39 }
  40
  41 #else
  42
  43 /* Thread local storage not supported through __thread,
  44  * use pthread_getspecific() instead. */
  45
  46 #include <pthread.h>
  47
  48 static pthread_key_t seed_key;
  49
  50 static void __attribute__((constructor))
  51 random_init(void)
  52 {
  53         pthread_key_create(&seed_key, NULL);
  54         fast_srandom(29264UL);
  55 }
  56
  57 void
  58 fast_srandom(unsigned long seed_)
  59 {
  60         pthread_setspecific(seed_key, (void *)seed_);
  61 }
  62
  63 unsigned long
  64 fast_getseed(void)
  65 {
  66         return (unsigned long)pthread_getspecific(seed_key);
  67 }
  68
  69 uint16_t
  70 fast_random(unsigned int max)
  71 {
  72         unsigned long pmseed = (unsigned long)pthread_getspecific(seed_key);
  73         pmseed = ((pmseed * 1103515245) + 12345) & 0x7fffffff;
  74         pthread_setspecific(seed_key, (void *)pmseed);
  75         return ((pmseed & 0xffff) * max) >> 16;
  76 }
  77
  78 float
  79 fast_frandom(void)
  80 {
  81         /* Construct (1,2) IEEE floating_t from our random integer */
  82         /* http://rgba.org/articles/sfrand/sfrand.htm */
  83         unsigned long pmseed = (unsigned long)pthread_getspecific(seed_key);
  84         pmseed *= 16807;
  85         union { unsigned long ul; floating_t f; } p;
  86         p.ul = ((pmseed & 0x007fffff) - 1) | 0x3f800000;
  87         pthread_setspecific(seed_key, (void *)pmseed);
  88         return p.f - 1.0f;
  89 }
  90
  91 #endif