src/core/random.c

   1 /** @file
   2  *
   3  * Random number generation
   4  *
   5  */
   6
   7 FILE_LICENCE ( GPL2_OR_LATER );
   8
   9 #include <stdlib.h>
  10 #include <gpxe/timer.h>
  11
  12 static int32_t rnd_seed = 0;
  13
  14 /**
  15  * Seed the pseudo-random number generator
  16  *
  17  * @v seed              Seed value
  18  */
  19 void srandom ( unsigned int seed ) {
  20         rnd_seed = seed;
  21 }
  22
  23 /**
  24  * Generate a pseudo-random number between 0 and 2147483647L or 2147483562?
  25  *
  26  * @ret rand            Pseudo-random number
  27  */
  28 long int random ( void ) {
  29         int32_t q;
  30
  31         if ( ! rnd_seed ) /* Initialize linear congruential generator */
  32                 srandom ( currticks() );
  33
  34         /* simplified version of the LCG given in Bruce Schneier's
  35            "Applied Cryptography" */
  36         q = ( rnd_seed / 53668 );
  37         rnd_seed = ( 40014 * ( rnd_seed - 53668 * q ) - 12211 * q );
  38         if ( rnd_seed < 0 )
  39                 rnd_seed += 2147483563L;
  40         return rnd_seed;
  41 }