src/core/random.c

   1 /** @file
   2  *
   3  * Random number generation
   4  *
   5  */
   6
   7 #include <stdlib.h>
   8
   9 static int32_t rnd_seed = 0;
  10
  11 /**
  12  * Seed the pseudo-random number generator
  13  *
  14  * @v seed              Seed value
  15  */
  16 void srandom ( unsigned int seed ) {
  17         rnd_seed = seed;
  18 }
  19
  20 /**
  21  * Generate a pseudo-random number between 0 and 2147483647L or 2147483562?
  22  *
  23  * @ret rand            Pseudo-random number
  24  */
  25 long int random ( void ) {
  26         int32_t q;
  27
  28         if ( ! rnd_seed ) /* Initialize linear congruential generator */
  29                 srandom ( currticks() );
  30
  31         /* simplified version of the LCG given in Bruce Schneier's
  32            "Applied Cryptography" */
  33         q = ( rnd_seed / 53668 );
  34         rnd_seed = ( 40014 * ( rnd_seed - 53668 * q ) - 12211 * q );
  35         if ( rnd_seed < 0 )
  36                 rnd_seed += 2147483563L;
  37         return rnd_seed;
  38 }