bug#74476: [PATCH] Explore JPEG loading without quantization

[Manuel Giraud via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Alan Third <alan@idiocy.org> writes:

> On Sat, Nov 30, 2024 at 06:25:01PM +0100, Manuel Giraud wrote:
>> Here is a new version with Alan suggestions.
>> 
>> FTR, the gain is much less interesting.  Here is the new timing with
>> same benchmark (see below):
>> (4.381739669 1 0.1034133749999997)
>
> That's unfortunate, although here I see an improvement of greater than
> 2x. Probably I could do with finding some larger images as the whole
> thing completes in under a second even without your patch.
>
> I've had a quick dig into lookup_rgb_color and assuming you have a
> true colour display and there's no gamma calculation going on (I don't
> know when that happens) it shouldn't be doing a whole lot more.
> Perhaps it's just the extra over-head of calling a function?

I also have a quick look at lookup_rgb_color and it seems to me that if
the user has a true color display (I suspect almost everyone nowadays),
we can spare the computation ct_hash_rgb and hence also spare to
allocate a ct_table.  WDYT?
-- 
Manuel Giraud