Subversion Repositories planix.SVN

#include "all.h"

/*
 *      algorithm by
 *      D. P. Mitchell & J. A. Reeds
 */
enum {
        LEN     = 607,
        TAP     = 273,
        MASK    = 0x7fffffffL,
        A       = 48271,
        M       = 2147483647,
        Q       = 44488,
        R       = 3399,
};

#define NORM    (1.0/(1.0+MASK))

static  ulong   rng_vec[LEN];
static  ulong*  rng_tap = rng_vec;
static  ulong*  rng_feed = 0;
static  Lock    lk;

static void
isrand(long seed)
{
        long lo, hi, x;
        int i;

        rng_tap = rng_vec;
        rng_feed = rng_vec+LEN-TAP;
        seed %= M;
        if(seed < 0)
                seed += M;
        if(seed == 0)
                seed = 89482311;
        x = seed;
        /*
         *      Initialize by x[n+1] = 48271 * x[n] mod (2**31 - 1)
         */
        for(i = -20; i < LEN; i++) {
                hi = x / Q;
                lo = x % Q;
                x = A*lo - R*hi;
                if(x < 0)
                        x += M;
                if(i >= 0)
                        rng_vec[i] = x;
        }
}

void
srand(long seed)
{
        lock(&lk);
        isrand(seed);
        unlock(&lk);
}

long
lrand(void)
{
        ulong x;

        lock(&lk);

        rng_tap--;
        if(rng_tap < rng_vec) {
                if(rng_feed == 0) {
                        isrand(1);
                        rng_tap--;
                }
                rng_tap += LEN;
        }
        rng_feed--;
        if(rng_feed < rng_vec)
                rng_feed += LEN;
        x = (*rng_feed + *rng_tap) & MASK;
        *rng_feed = x;

        unlock(&lk);
        return x;
}