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#include <stdlib.h>
/*
* 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
typedef unsigned long ulong;
static ulong rng_vec[LEN];
static ulong* rng_tap = rng_vec;
static ulong* rng_feed = 0;
void
srand(unsigned int 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;
}
}
static long
lrand(void)
{
ulong x;
rng_tap--;
if(rng_tap < rng_vec) {
if(rng_feed == 0) {
srand(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;
}
int
rand(void)
{
return lrand() & 0x7fff;
}
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