musl - Re: roundf() (and round(), and ...)

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Message-ID: <b03ae0d7-3673-b2fa-44c-bd7e6a689bb6@esi.com.au>
Date: Fri, 21 Jun 2024 18:12:22 +1000 (AEST)
From: Damian McGuckin <damianm@....com.au>
To: MUSL <musl@...ts.openwall.com>
Subject: Re: roundf() (and round(), and ...)

There is an optimization in roundf() (and an equivalent in round())
which handles the case of numbers 0 < |x| < 0.5

     if (e < 0x7f-1) {
         return 0*u.f;
     }

If one has lots of numbers close to zero (as you would if you were testing 
even possible 32-bit floating point number or for any other reason), this
can mean a total run time is 5% faster overall (at the expense of the 
performance of cases for |x| >= 0.5.

Is such an optimization worth it? And yes, we re not talking about lots of
compute cycles here!

Thanks - Damian

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