> I need to do sin() and cos() functions in a PIC chip, but much faster
> than the 3 ms time required by the CCS C compiler. Any advice on how
> this is done with less precision and much more speed? I need
> three-byte integers.

For small angles sine(X) = X (in radians) to a good approximation.
Accuracy depends on how large you let X get.
You can probably play with symmetries above and below 45 degrees.

Accuracy (if my Excelling is correct)

Bits Accuracy
            X degrees

11        3 degrees
10        4 degrees
9          6 degrees
8          9 degrees
7        12
6        17
5        24
4        34
3        48
2        64        :-)



You may be able to use identities to allow dealing in only small angles, but
the processing cost may offset any gains.

eg sin(2x) = 2.sinx.cosx
You can repeat this to again reduce the angle but the multiplications get
costly.



        Russell McMahon

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