random.c

这是TFTP 协议的最新源代码 很辛苦的

/* from http://remus.rutgers.edu/~rhoads/Code/tt800.c */

/***********************************************************************
  can return either a random 32-bit integer or a random float in [0 1)
  period = 2^800
***********************************************************************/

#include "baselib.h"

#define N 25
#define M 7

static unsigned int x[N];		/* the 25 seeds */
static const unsigned int mag01[2] = { 0x0, 0x8ebfd028 };	/* "magic" vector */
static int ks;

void srand(unsigned int seed)
{
	int k;

	ks = 0;
	x[0] = (seed | 1);
	for (k = 1; k < N; k++)
		x[k] = (69069 * x[k - 1]);
}

unsigned int rand(void)
{
	unsigned int y;
	int k;

	if (ks == N) {
		for (k = 0; k < N - M; k++)
			x[k] = x[k + M] ^ (x[k] >> 1) ^ mag01[x[k] & 1];

		for (; k < N; k++)
			x[k] = x[k + (M - N)] ^ (x[k] >> 1) ^ mag01[x[k] & 1];

		ks = 0;
	}
	y = x[ks++];
	y ^= (y << 7) & 0x2b5b2500;
	y ^= (y << 15) & 0xdb8b0000;
	y ^= (y >> 16);
	return y;
}