sincos is useful in general. Rotations for example often need sine and cosine of the same angle. Because transcendental functions are implemented as a microcod

sincos is useful in general. Rotations for example often need sine and cosine of the same angle. Because transcendental functions are implemented as a microcode loop, a sincos instruction lets you cut in half the loop overhead. If the overhead were 50% (e.g. 100 cycles arithmetic and 50 cycles overhead) you could cut sincos to 250 cycles, for an overhead of only 25%.