Hi Oren,
I once read about something called CORDIC (Co-Ordinate Rotation DIgital Computing)... its a method of calculating trig functions through simple shift and add/subtract operations and I think a look-up table is involved. You could look it up and see if it is usable on '51.

The other way is to use a look-up table straight out... but it could get a little memory intensive

But CORDIC looks pretty impressive, besides trig functions it may even be applicable to multi-byte math and complex math. In fact I think Peter's method looks a lot like a CORDIC algorithm!

Check out this link:
http://www.chipcenter.com/circuitce...00rp48.htm

There's also a CORDIC FAQ at dspguru.com
http://www.dspguru.com/info/faqs/cordic.htm

kundi