Re: [PATCH v2] drm/color: Document CTM eqations
From: Ville Syrjälä
Date: Fri Feb 17 2017 - 09:56:56 EST
On Fri, Feb 17, 2017 at 02:42:26PM +0000, Lionel Landwerlin wrote:
> On 17/02/17 13:54, Brian Starkey wrote:
> > What's the verdict? We've got  which is about to become another
> > (driver) implementation - better to change before that merges than
> > after I guess.
> > -Brian
> >  https://lkml.org/lkml/2017/2/13/304
> > On Wed, Feb 15, 2017 at 11:56:55AM +0000, Daniel Stone wrote:
> >> Hi,
> >> On 15 February 2017 at 11:39, Ville Syrjälä
> >> <ville.syrjala@xxxxxxxxxxxxxxx> wrote:
> >>> On Tue, Jan 31, 2017 at 06:46:39PM +0100, Daniel Vetter wrote:
> >>>> On Tue, Jan 31, 2017 at 6:22 PM, Ville Syrjälä
> >>>> <ville.syrjala@xxxxxxxxxxxxxxx> wrote:
> >>>> > Hmm. Two's complement is what I was thinking it is. Which shows that
> >>>> > I never managed to read the code in any detail. Definitely needs to
> >>>> > be documented properly.
> >>>> That sounds supremely backwards. I guess we can't fix this anymore?
> >>> I have no idea. Anyone else?
> >> I don't know of any implementation using this; maybe closed Intel
> >> Android stuff? Certainly GitHub showed no-one using it, and neither X
> >> nor Weston/Mutter are using it yet.
> >> Cheers,
> >> Daniel
> If we're talking fixed point reprsentation, ChromeOS is using this :
So it's already using the sign+magnitude stuff. Which presumably
means we can't change it to two's complement anymore :( Maybe we add a
CTM2 property ;)
Using sign+magnitude definitely looks rather inefficient since there's
a branch inside the loop. With two's complement you wouldn't need that
thing slowing you down.