RE: [Intel-gfx] [PATCH 1/4] drm: Fix color LUT rounding

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> -----Original Message-----
> From: Borah, Chaitanya Kumar
> Sent: Monday, November 20, 2023 6:33 PM
> To: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx; Jani
> Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> Subject: RE: [Intel-gfx] [PATCH 1/4] drm: Fix color LUT rounding
> 
> Hello Ville,
> 
> > -----Original Message-----
> > From: dri-devel <dri-devel-bounces@xxxxxxxxxxxxxxxxxxxxx> On Behalf Of
> > Ville Syrjälä
> > Sent: Tuesday, October 31, 2023 9:37 PM
> > To: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> > Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > Subject: Re: [Intel-gfx] [PATCH 1/4] drm: Fix color LUT rounding
> >
> > On Tue, Oct 31, 2023 at 11:15:35AM +0200, Jani Nikula wrote:
> > > On Fri, 13 Oct 2023, Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx> wrote:
> > > > entrirely. But perhaps a better idea would be to follow the OpenGL
> > > > int<->float conversion rules, in which case we get the following
> > > > results:
> > >
> > > Do you have a pointer to the rules handy, I couldn't find it. :(
> >
> > Eg. '2.3.5 Fixed-Point Data Conversions' in GL 4.6 spec. The section
> > number probably changes depending on which version of the spec you look
> at.
> >
> 
> This section particularly talks about conversion of normalized fixed point  to
> floating point numbers and vice versa.
> Pardon my limited knowledge on the topic but aren't we just doing a scaling
> factor conversion(Q0.16 -> Q0.8) in these patches?
> 
> I could not draw a direct relation between the formulas in the section[1] and
> what we are doing here.(but it could be just me!)

Scratch that! As I understand, in effect we are doing a Q0.16 Fixed Point -> Floating point -> Q0.8 Fixed Point conversion.
Correct me if I am wrong! Otherwise

LGTM.

Reviewed-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@xxxxxxxxx>


> 
> Regards
> 
> Chaitanya
> 
> [1] https://registry.khronos.org/OpenGL/specs/gl/glspec46.core.pdf '2.3.5
> Fixed-Point Data Conversions'
> 
> > >
> > > Might also add the reference to the commit message and/or comment.
> > >
> > > BR,
> > > Jani.
> > >
> > > --
> > > Jani Nikula, Intel
> >
> > --
> > Ville Syrjälä
> > Intel




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