OT : Approximate / fast math libraries ?

[Chris Jones <jonesc hep phy cam ac uk>]

Hi,

I have a number crunch application that is starting to hit bottlenecks 
in standard maths functions, like log, exp sqrt etc. Thing is, in many 
places I don't need much precision, so was wondering if there was 
anything I could do, like use a different library or enable some gcc 
options (currently using -O2) to speed things up.

Does anyone have any recommendations for fast maths ? search around on 
the web I've found a lot of references to fast / approximate math 
libraries, but nothing obvious.

Chris