GNU bug report logs - #41544
26.3; Possible incorrect results from color-distance

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From: Eli Zaretskii <eliz <at> gnu.org>
To: Mattias Engdegård <mattiase <at> acm.org>
Cc: tom <at> tromey.com, simon <at> polaris64.net, 41544 <at> debbugs.gnu.org
Subject: bug#41544: 26.3; Possible incorrect results from color-distance
Date: Wed, 03 Jun 2020 17:24:56 +0300

> From: Mattias Engdegård <mattiase <at> acm.org>
> Date: Tue, 2 Jun 2020 22:41:03 +0200
> Cc: tom <at> tromey.com, simon <at> polaris64.net, 41544 <at> debbugs.gnu.org
> 
> > I'd prefer to fix only the symmetry bug (which AFAIU happens because
> > we use bit shifts on signed integers), without introducing any other
> > effects on the function's behavior and return values.  AFAIU, such a
> > fix should not require any changes outside of the function itself.
> 
> Very well, it is obviously an improvement. The reason for the current asymmetry was actually that the algorithm discarded the low bits; what about fixing that as well?

Sure, let's make it as accurate as the return value allows.

> The improved accuracy amounts to less than 1 % of difference in the return value; no other code needs changing, and we get the symmetry for free. Proposed patch attached.

Not sure I understand completely: does this patch make the function
symmetric?  If so, what additional improvements did you have in mind
when you mentioned more fixing above?

Thanks.

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