void xorshift(unsigned int w,unsigned int h,unsigned int **R,unsigned int seed)
{
    unsigned int r,k;
    r=seed;
    *R=malloc(sizeof(unsigned int)*(2*w*h-1));
    for (k=1;k<2*w*h;k++)
    {
        r=r^r<<13;
        r=r^r>>17;
        r=r^r<<5;
        (*R)[k]=r;
        //printf("%u\n",r);
    }
}