bug#41544: 26.3; Possible incorrect results from color-distance

[Eli Zaretskii]

> From: Mattias Engdegård <mattiase@acm.org>
> Date: Tue, 2 Jun 2020 22:41:03 +0200
> Cc: tom@tromey.com, simon@polaris64.net, 41544@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.