[Pixman] Faster unorm_to_unorm for wide path processing
Antti S. Lankila
alankila at bel.fi
Sun Jun 10 10:33:01 PDT 2012
On 10.06.2012 20:03, Søren Sandmann wrote:
> "Antti S. Lankila"<alankila at bel.fi> writes:
>> Attached is a simple patch that produces around 20 % Mpix/s
>> improvement for wide path processing due to significant optimization
>> of pixman_expand. On my i7 laptop, we go from:
>>> src_8888_2x10 = L1: 62.08 L2: 60.73 M: 59.61
>>> ( 4.30%) HT: 46.81 VT: 42.17 R: 43.18 RT: 26.01 (
>>> src_8888_2x10 = L1: 76.94 L2: 78.43 M: 75.87
>>> ( 5.59%) HT: 56.73 VT: 52.39 R: 53.00 RT: 29.29 (
>> The key of the patch is the observation that unorm_to_unorm's work can
>> more easily be done with a simple multiplication and shift, when the
>> function is applied repeatedly and the parameters are not compile-time
>> constants. For instance, converting from 0xfe to 0xfefe (expanding
>> from 8 bits to 16 bits) can be done by calculating
>> c = c * 0x101
>> However, sometimes the result is not a neat replication of all the
>> bits. For instance, going from 10 bits to 16 bits can be done by
>> c = c * 0x401UL>> 4
>> where the intermediate result is 20 bit wide repetition of the 10-bit
>> pattern followed by shifting off the unnecessary lowest bits.
>> The patch has the algorithm to calculate the factor and the shift, and
>> converts the code to use it.
> This patch looks basically good to me provided that make check still
> passes. The comments I have are mainly about coding style (please see
> the CODING_STYLE file). In particular:
> - All the information in the mail would be useful to have in the commit
> message: the speed-up, how it works, etc.
Okay, adapted the commit message on the patch from the mailing list posting.
> - The function unorm_to_unorm_params() should be static
> - Space before the left parenthesis
> - Avoid variable declarations in the middle of the code
> - Indent is four spaces
> - Braces go on their own line
Thanks for the code review. This new patch (attached) should have all of
these accounted for.
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