>>Hi y'all -
>>I have a need for an fast exp(x) function...
>>x is a float and can range inside +-10.0.
You can calculate exp(x) in fixed-point with a series of shifts
and adds and a small lookup table using CORDIC iterations.
Convergence is linear, so you get about one bit of precision with
each iteration through a simple loop. With 32-bit words, you can
probably get 26 bits of precision. If you can get by with less
bits of precision, you can by with less iterations.
I don't have the references handy, but I just recently published
a paper in Graphics Gems (Academic Press, 1990) on CORDIC trigonometry.
In the references to that paper are pointer to papers by Walthers
and Chen which address exp, log, sqrt, and a host of other nonlinear