The underlying Xilinx CORDIC IP uses 2 bits for the whole part of its
(X,Y) inputs and its magnitude output. So, having 17 bits means we have
enough precision to represent the entire range of an sc16. The 16-bit
CORDIC is insufficient to cover this entire range.
Original-commit: 0d3d69493aac9239ae437b04f291c61669678606
