random.c

   1 #include <stdio.h>
   2
   3 #include "random.h"
   4
   5
   6 /* Simple Park-Miller */
   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         unsigned long hi, lo;
  28         lo = 16807 * (pmseed & 0xffff);
  29         hi = 16807 * (pmseed >> 16);
  30         lo += (hi & 0x7fff) << 16;
  31         lo += hi >> 15;
  32         pmseed = (lo & 0x7fffffff) + (lo >> 31);
  33         return ((pmseed & 0xffff) * max) >> 16;
  34 }
  35
  36 float
  37 fast_frandom(void)
  38 {
  39         /* Construct (1,2) IEEE float from our random integer */
  40         /* http://rgba.org/articles/sfrand/sfrand.htm */
  41         union { unsigned long ul; float f; } p;
  42         p.ul = (((pmseed *= 16807) & 0x007fffff) - 1) | 0x3f800000;
  43         return p.f - 1.0f;
  44 }
  45
  46 #else
  47
  48 /* Thread local storage not supported through __thread,
  49  * use pthread_getspecific() instead. */
  50
  51 #include <pthread.h>
  52
  53 static pthread_key_t seed_key;
  54
  55 static void __attribute__((constructor))
  56 random_init(void)
  57 {
  58         pthread_key_create(&seed_key, NULL);
  59         fast_srandom(29264UL);
  60 }
  61
  62 void
  63 fast_srandom(unsigned long seed_)
  64 {
  65         pthread_setspecific(seed_key, (void *)seed_);
  66 }
  67
  68 unsigned long
  69 fast_getseed(void)
  70 {
  71         return (unsigned long)pthread_getspecific(seed_key);
  72 }
  73
  74 uint16_t
  75 fast_random(unsigned int max)
  76 {
  77         unsigned long pmseed = (unsigned long)pthread_getspecific(seed_key);
  78         unsigned long hi, lo;
  79         lo = 16807 * (pmseed & 0xffff);
  80         hi = 16807 * (pmseed >> 16);
  81         lo += (hi & 0x7fff) << 16;
  82         lo += hi >> 15;
  83         pmseed = (lo & 0x7fffffff) + (lo >> 31);
  84         pthread_setspecific(seed_key, (void *)pmseed);
  85         return ((pmseed & 0xffff) * max) >> 16;
  86 }
  87
  88 float
  89 fast_frandom(void)
  90 {
  91         /* Construct (1,2) IEEE float from our random integer */
  92         /* http://rgba.org/articles/sfrand/sfrand.htm */
  93         unsigned long pmseed = (unsigned long)pthread_getspecific(seed_key);
  94         pmseed *= 16807;
  95         union { unsigned long ul; float f; } p;
  96         p.ul = ((pmseed & 0x007fffff) - 1) | 0x3f800000;
  97         pthread_setspecific(seed_key, (void *)pmseed);
  98         return p.f - 1.0f;
  99 }
 100
 101 #endif