| 0,0 → 1,37 |
|---|
| #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); |
| } |