[Mesa-dev] [PATCH 11/29] mesa: Use bitmask/ffs to iterate enabled lights for building ff shader keys.

Ian Romanick idr at freedesktop.org
Wed May 25 16:13:46 UTC 2016

On 05/25/2016 03:06 AM, Erik Faye-Lund wrote:
> On Tue, May 24, 2016 at 8:42 AM,  <Mathias.Froehlich at gmx.net> wrote:
>> From: Mathias Fröhlich <mathias.froehlich at web.de>
>> Replaces a loop that iterates all lights and test
>> which of them is enabled by a loop only iterating over
>> the bits set in the enabled bitmask.
> This takes the code from something very obvious and easy to follow to
> something you'll have to think twice about the correctness of...
> Since MAX_LIGHTS is 8, this seems a bit like a premature optimization
> to me. Does this patch yield any measurable improvement in speed in
> any real-world applications?

Right... because now the compiler will likely not unroll the loop.  I'd
be curious to compare the before / after code.  My guess is that it
doesn't make much difference either way.

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