看uboot的时候发现随机数的另外一种算法

#include <stdio.h>
#include <time.h>

static unsigned int y = 1U;

unsigned int rand_r(unsigned int *seedp)
{
*seedp ^= (*seedp << 13);  //这里居然用异或和位移来实现，感觉很强大
*seedp ^= (*seedp >> 17);
*seedp ^= (*seedp << 5);
return *seedp;
}

unsigned int rand(void)
{
return rand_r(&y);
}

void srand(unsigned int seed)
{
y = seed;
}

int main(void)
{
int i  ;
srand(time(NULL)) ;
for(i = 0 ; i < 100 ; i++)
printf("%d\n", rand() % 100) ;
}