comiss vs. ucomiss

Vladimir Kozlov Vladimir.Kozlov at Sun.COM
Tue Oct 14 14:57:54 PDT 2008

Even if exceptions are masked CPU need some
logic to check it. I think, a program with
ucom will be faster if a data has a lot of QNaN.


Tom Rodriguez wrote:
> I was just making some comparisons between and and 
> noticed that uses comiss/comisd for floating point compares 
> with SSE but uses ucomiss/ucomisd.  The only difference 
> between them is that the ucom versions don't signal for quiet NaNs.  We 
> have fp exception suppressed so functionally it doesn't make any 
> difference.  It does seem like they should be doing the same thing 
> though.  Anyone know why they emit different things?
> tom

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