Reverse-engineering the Intel 8087's tangent algorithm: more than CORDIC

Reverse-engineering the tangent function of the Intel 8087 math coprocessor revealed that it uses a combination of CORDIC (Coordinate Rotation Digital Computer) and a polynomial approximation, but also introduces a clever optimization that reduces the number of iterations required for the CORDIC algorithm. The optimization, known as 'split CORDIC,' involves dividing the angle into two parts, one of which is processed using a standard CORDIC algorithm, while the other is handled using a simpler, more efficient method. This results in a significant reduction in the number of iterations required for the tangent calculation, making the 8087's implementation more efficient than a straight CORDIC algorithm.