On Thu, Feb 9, 2012 at 11:35 AM, Andrew Haley <a...@redhat.com> wrote: > On 02/09/2012 10:20 AM, James Courtier-Dutton wrote: >> From what I can see, on x86_64, the hardware fsin(x) is more accurate >> than the hardware fsincos(x). >> As you gradually increase the size of X from 0 to 10e22, fsincos(x) >> diverges from the correct accurate value quicker than fsin(x) does. >> >> So, from this I would say that using fsincos instead of fsin is not a >> good idea, at least on x86_64 platforms. > > That's true iff you're using the hardware builtins, which we're not on > GNU/Linux unless you're using -ffast-math. If you're using > -ffast-math, the fsincos optimization is appropriate anyway because > you want fast. If you're not using -ffast-math it's still > appropriate, because we're using an accurate libm.
The point of course is that glibc happily uses fsin/fsincos (which isn't even fast compared to a decent implementation using SSE math). Richard. > Andrew.
