static void Twist()
{
    uint32_t  i, x, xA;

    for ( i = 0; i < N; i++ )
    {
        x = (mt[i] & MASK_UPPER) + (mt[(i + 1) % N] & MASK_LOWER);

        xA = x >> 1;

        if ( x & 0x1 )
            xA ^= A;

        mt[i] = mt[(i + M) % N] ^ xA;
    }

    index = 0;
}