This is the mail archive of the libc-alpha@sourceware.org mailing list for the glibc project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: [PATCH 2/3] powerpc: POWER8 fmod optimization


On Wed, 12 Nov 2014, Adhemerval Zanella wrote:

> Indeed I overlook it, as I am seeing now with a more extensive testing.  
> Checking now, it seems using a FP division operation in the loop to 
> correct it not the best strategy to achieve better performance.

And there are other problems with the division I didn't notice previously.  
If the exponent difference is large enough, the division may overflow.  
And you're assuming the result of (round to next integer toward 0 (divide 
and round in current rounding mode)) is the same as (divide in infinite 
precision, round once to an integer toward 0) - but depending on the 
arguments and rounding mode, the result of the division may be rounded 
away from 0 to an integer with magnitude greater than the desired result.

-- 
Joseph S. Myers
joseph@codesourcery.com


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]