Re: callgrind and sin/cos under GCC

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Markus wrote:
> BTW, s_sincos.S was removed from glibc a while ago. So if you're running
> a recent glibc version you end up with the slow floating-point sin/cos
> implementation, that causes a 50% slowdown.
> See: http://sourceware.org/bugzilla/show_bug.cgi?id=14412
>
> However Intel has recently posted fast SSE sin/cos/sincos versions for
> libm (sinf, cosf and sincosf). I think gcc should be updated to call
> those instead.

Correction on my part, we're using Ubuntu 11.10, which uses glibc 2.13.

So if I'm reading at the various ChangeLogs and BugZilla's correctly,
we should still have the s_sincos.S impl (we don't have large inputs,
so we're not seeing any problems).  This s_sincos.S calls fsincos (X87
instruction?).

The reason this came up is we were comparing the profiling results we
got under Visual Studio (using AMD Code Analyst) and while generally
the profiling was consistent, the call to sincos (and atan2) was
taking quite a bit more relative time than with Visual Studio.  So
we're basically digging to try and figure out why.

Would Intel's SSE2 version make any difference in this case?  (we're
using doubles, not floats).

Thanks,
Pete


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