OT : Approximate / fast math libraries ?

[Chris Jones]

> Another poster mentioned that pentiums
> have hardware instructions for trig functions.
> If you are using them, there isn't much hope for speed up.

Out of interest, whats needs to be done to use these, some gcc flag ? My 
profiling suggests that atan2(x,y) is taking ~ 50% of some method speed. Yes, 
the methods is already fast, but still is this reasonable if hardware 
instructions are being used. Is there some way I can check to see exactly 
what is used ?

> These formulas will probably not be useful unless
> you know in advance the ranges of their arguments.

Yes, I considered coding up my own methods along this line, but figured 
getting it correct was not a small amount of effort, and was hoping to find 
some project that had done it for me.

cheers Chris