private void Theta(ulong[] A)
{
for (int x = 0; x < 5; x++)
{
C[x] = 0;
for (int y = 0; y < 5; y++)
{
C[x] ^= A[x + 5 * y];
}
}
for (int x = 0; x < 5; x++)
{
ulong dX = ((((C[(x + 1) % 5]) << 1) ^ ((C[(x + 1) % 5]) >> (64 - 1)))) ^ C[(x + 4) % 5];
for (int y = 0; y < 5; y++)
{
A[x + 5 * y] ^= dX;
}
}
}