Subversion Repositories openrisc

#include <stdlib.h>

/* Pseudo-random generator based on Minimal Standard by

   Lewis, Goodman, and Miller in 1969.

   I[j+1] = a*I[j] (mod m)

   where a = 16807

         m = 2147483647

   Using Schrage's algorithm, a*I[j] (mod m) can be rewritten as:

     a*(I[j] mod q) - r*{I[j]/q}      if >= 0

     a*(I[j] mod q) - r*{I[j]/q} + m  otherwise

   where: {} denotes integer division

          q = {m/a} = 127773

          r = m (mod a) = 2836

   note that the seed value of 0 cannot be used in the calculation as

   it results in 0 itself

*/

int

_DEFUN (rand_r, (seed), unsigned int *seed)

{

        long k;

        long s = (long)(*seed);

        if (s == 0)

          s = 0x12345987;

        k = s / 127773;

        s = 16807 * (s - k * 127773) - 2836 * k;

        if (s < 0)

          s += 2147483647;

        (*seed) = (unsigned int)s;

        return (int)(s & RAND_MAX);

}