Log Library - How is it done in the library code?

[Anil Joshi]

I need to compute natural log for some numbers. I could use the c math.h library
routine but I do not want the accuracy of the library routine. A crude 
approximation would suffice. Does anyone know how this is done in the c library
routine? Is it possible to get the source code?
Thanks
Anil
-- 
"Come the (computer) revolution, all persons found guilty of such criminal
behaviour will be summarily executed, and their programs won't be!"
- Press, Flannerty, Teukolsky and Vetterling