f2xm1

Why does it subtract 1, and why does it only work for values between [-1,1] ?
Furthermore why does cos take so much longer to calculate than sin when cos is just sin(x+pi/2)?

BECAUSE WHEN SIN IS SLOW COS IS FAST, AND WHEN COS IS SLOW SIN IS FAST.

IF YOU WANT TO CALC SIN AND COS USE FSINCOS INSTRUCTION OF THE MATEMATIC COPROCESSOR TO CALC BOTH AT COST OF ONE!