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c6fbb6bca1
The current implementation of drm_color_lut_extract() generates weird results. Eg. if we go through all the values for 16->8bpc conversion we see the following pattern: in out (count) 0 - 7f -> 0 (128) 80 - 17f -> 1 (256) 180 - 27f -> 2 (256) 280 - 37f -> 3 (256) ... fb80 - fc7f -> fc (256) fc80 - fd7f -> fd (256) fd80 - fe7f -> fe (256) fe80 - ffff -> ff (384) So less values map to 0 and more values map 0xff, which doesn't seem particularly great. To get just the same number of input values to map to the same output values we'd just need to drop the rounding entrirely. But perhaps a better idea would be to follow the OpenGL int<->float conversion rules, in which case we get the following results: in out (count) 0 - 80 -> 0 (129) 81 - 181 -> 1 (257) 182 - 282 -> 2 (257) 283 - 383 -> 3 (257) ... fc7c - fd7c -> fc (257) fd7d - fe7d -> fd (257) fe7e - ff7e -> fe (257) ff7f - ffff -> ff (129) Note that since the divisor is constant the compiler is able to optimize away the integer division in most cases. The only exception is the _ULL() case on 32bit architectures since that gets emitted as inline asm via do_div() and thus the compiler doesn't get to optimize it. Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20231013131402.24072-2-ville.syrjala@linux.intel.com Reviewed-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com> Reviewed-by: Jani Nikula <jani.nikula@intel.com> Acked-by: Maxime Ripard <mripard@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.