Job Noorman 6d59a3e3e7 nir/lower_alu: use Knuth's Algorithm M for [iu]mul_high
This significantly simplifies the handling of signed numbers as the same
code path can handle signed and unsigned numbers by simply using ishr
instead of ushr for some of the shifts. For both cases, the number of
additions and shifts are also reduced.

Note that LLVM uses the same algorithm.

fossil-db stats for Turnip:

Totals from 4849 (2.94% of 164705) affected shaders:
MaxWaves: 52318 -> 52332 (+0.03%); split: +0.04%, -0.02%
Instrs: 5262458 -> 5218922 (-0.83%); split: -0.87%, +0.05%
CodeSize: 10831900 -> 10655170 (-1.63%); split: -1.64%, +0.01%
NOPs: 829481 -> 836010 (+0.79%); split: -0.95%, +1.74%
MOVs: 176187 -> 173788 (-1.36%); split: -3.27%, +1.91%
COVs: 104096 -> 86543 (-16.86%); split: -16.87%, +0.01%
Full: 90434 -> 90158 (-0.31%); split: -0.33%, +0.03%
(ss): 131091 -> 130866 (-0.17%); split: -0.87%, +0.70%
(sy): 55550 -> 55769 (+0.39%); split: -0.92%, +1.32%
(ss)-stall: 406003 -> 407194 (+0.29%); split: -1.10%, +1.39%
(sy)-stall: 1668213 -> 1678082 (+0.59%); split: -1.31%, +1.90%
Preamble Instrs: 1105270 -> 1067290 (-3.44%); split: -3.50%, +0.06%
Constlen: 423776 -> 423560 (-0.05%)
Last helper: 1038202 -> 1035540 (-0.26%); split: -0.42%, +0.16%
Last baryf: 38908 -> 38632 (-0.71%)
Subgroup size: 336640 -> 336832 (+0.06%)
Cat0: 916209 -> 922848 (+0.72%); split: -0.87%, +1.59%
Cat1: 282813 -> 262845 (-7.06%); split: -7.49%, +0.43%
Cat2: 2198715 -> 2183012 (-0.71%); split: -0.72%, +0.01%
Cat3: 1390914 -> 1376421 (-1.04%)
Cat7: 123127 -> 123116 (-0.01%); split: -0.24%, +0.23%

Signed-off-by: Job Noorman <jnoorman@igalia.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37793>
2025-10-10 05:31:17 +00:00
2025-02-23 00:31:59 +01:00
2025-10-09 12:12:42 +00:00
2025-10-09 10:12:05 -07:00
2025-09-26 14:02:52 +00:00
2025-01-08 20:37:51 +00:00
2023-11-02 11:37:46 +00:00
2025-09-16 19:45:15 +00:00
2025-08-31 15:38:27 +00:00
2024-11-18 22:29:14 +00:00
2025-07-16 13:50:24 +00:00

`Mesa <https://mesa3d.org>`_ - The 3D Graphics Library
======================================================


Source
------

This repository lives at https://gitlab.freedesktop.org/mesa/mesa.
Other repositories are likely forks, and code found there is not supported.


Build & install
---------------

You can find more information in our documentation (`docs/install.rst
<https://docs.mesa3d.org/install.html>`_), but the recommended way is to use
Meson (`docs/meson.rst <https://docs.mesa3d.org/meson.html>`_):

.. code-block:: sh

  $ meson setup build
  $ ninja -C build/
  $ sudo ninja -C build/ install

Support
-------

Many Mesa devs hang on IRC; if you're not sure which channel is
appropriate, you should ask your question on `OFTC's #dri-devel
<irc://irc.oftc.net/dri-devel>`_, someone will redirect you if
necessary.
Remember that not everyone is in the same timezone as you, so it might
take a while before someone qualified sees your question.
To figure out who you're talking to, or which nick to ping for your
question, check out `Who's Who on IRC
<https://dri.freedesktop.org/wiki/WhosWho/>`_.

The next best option is to ask your question in an email to the
mailing lists: `mesa-dev\@lists.freedesktop.org
<https://lists.freedesktop.org/mailman/listinfo/mesa-dev>`_


Bug reports
-----------

If you think something isn't working properly, please file a bug report
(`docs/bugs.rst <https://docs.mesa3d.org/bugs.html>`_).


Contributing
------------

Contributions are welcome, and step-by-step instructions can be found in our
documentation (`docs/submittingpatches.rst
<https://docs.mesa3d.org/submittingpatches.html>`_).

Note that Mesa uses gitlab for patches submission, review and discussions.
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