nemesis xorshift

typedef struct
{
    uint32 seed;
    uint32 rs [4];
} xor_t;

static xor_t internal;

void xsrand (uint32 seed)
{
    xsrand_r (&internal, seed);
    return;
}

void xsrand_r (xor_t *x, uint32 seed)
{
    if (!seed)
        x->rs [0] = seed - 1;
    else
        x->rs [0] = seed;

    x->seed = x->rs [0];

    x->rs [1] = x->rs [0] << 1;
    x->rs [2] = x->rs [1] << 1;
    x->rs [3] = x->rs [2] << 1;

    return;
}

uint32 xrand (void)
{
    return xrand_r (&internal);
}

uint32 xrand_r (xor_t *x)
{
    register uint32 tmp;

    tmp = x->rs [0] ^ (x->rs [0] << 4);

    x->rs [0] = x->rs [1];
    x->rs [1] = x->rs [2];
    x->rs [2] = x->rs [3];

    return x->rs [3] = (x->rs [3] ^ (x->rs [3] >> 13)) ^ (tmp ^ (tmp >> 13));
}