Re: Sine function Message #2 Posted by Andrés C. Rodríguez on 16 Apr 2000, 8:19 p.m., in response to message #1 by Jack Auman
The calculators may use a combination of lookup tables for certain values, and also use some kind of series or polynomial expansion to obtain the values for all other angles. Also needed are: normalization of the angle (reducing it to +/180°); conversion between grad/rad/deg; use and truncation of guard digits; and checking for particular conditions (tangent of 90°, etc). These are the steps programmed in the calculator ROM or (not exactly named) microcode. In the HP Journal, between 1972 and 1977, some four or five articles appeared, detailing the methods chosen by the calculators designers for trig and log functions, and the tradeoffs between execution time, error magnitude, and ROM space needed to implement them.
