A sin/cos generator which stores values for sin X and cos X, multiplies the sin X and cos X by the value sin Y to produce partial products -sin Y sin X and sin Y cos X and adds the partial products sin Y cos X to sin X to produce sin (X+Y) and adds the partial products -sin Y sin X to cos X to produce cos (X+Y). The values of sin X and cos X are stored for a single quadrant without sign designation and quadrant control is provided to complement the appropriate values of sin X and cos X before adding and multiplying. The complementing forms the one's complement and adds a 1 in the least significant bit to form the two's complement.