#include	<u.h>#include	<libc.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#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 voidisrand(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;	}} voidsrand(long seed){	lock(&lk);	isrand(seed);	unlock(&lk);} longlrand(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;}