[Pixman] Faster unorm_to_unorm for wide path processing

[Antti S. Lankila]

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 (
>>>                    325Kops/s)
>> to
>>
>>>   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 (
>>>                    363Kops/s)
>> 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
>> calculating
>>
>> 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.

-- 
Antti