Subversion Repositories planix.SVN

/*
 * libc pseudo-random number generators, but without locks.
 */
#include        "u.h"
#include        "../port/lib.h"
#include        "mem.h"
#include        "dat.h"
#include        "fns.h"
#include        "io.h"
#include        "ureg.h"
#include        "pool.h"

/* stubs to emulate random.c */
ulong
randomread(void *, ulong)
{
        return 0;
}

void
randominit(void)
{
}

/*
 *      algorithm by
 *      D. P. Mitchell & J. A. Reeds
 */

#define LEN     607
#define TAP     273
#define MASK    0x7fffffffL
#define A       48271
#define M       2147483647
#define Q       44488
#define 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 void
isrand(long seed)
{
        long lo, hi, x;
        int i;

        rng_tap = rng_vec;
        rng_feed = rng_vec+LEN-TAP;
        seed = 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)
{
        isrand(seed);
}

long
lrand(void)
{
        ulong x;

        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;
        return x;
}