[Pixman] Pixman library on wince arm

Siarhei Siamashka siarhei.siamashka at gmail.com
Thu Sep 30 01:27:18 PDT 2010

On Thursday 30 September 2010 00:29:14 PS wrote:
> int over_n_dst_ps (int alpha, int color, int dst_color)
> {
>    int q0 = 0xff - alpha;
>    int q1 = color * alpha + 0x80;
>    int u = dst_color * q0 + q1;
>    return (u + (u >> 8)) >> 8;
> }
> does not generate any asserts and
> stddev_pixman = 0.405459
> stddev_ps = 0.287262
> As you can see my math isn't much different from pixman; 

Yes, because it is clearly not your math from [1] anymore. Now there are also
two shifts involved instead of one. I would like to see what kind of neon
assembly you are doing to use here and whether it can be actually implemented
with less instructions than "vmull.u8 / vrshr.u16 / vraddhn.i16 / vqadd.u8"
from the current pixman code.

When proposing some improvements for pixman, please send the patches or at
least compilable test programs. That'll save a lot of time and help to avoid
any possible misunderstandings. After all, the "winner" is the one who can
introduce correct, well performing and testable code which is suitable to be
pushed to pixman source repository ;) There is a lot of fun stuff to work on
and many things still can be improved.

Regarding the topic of this discussion in general. Is pixman currently usable
on wince arm? Is it easy to build? Does it need any patches/fixes?

1. http://lists.freedesktop.org/archives/pixman/2010-September/000626.html

Best regards,
Siarhei Siamashka
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