[Pixman] fast-scale branch performance improvements

[Alexander Larsson]

In the spice project we use pixman for a bunch of stuff, including
nearest scaling of video. Today i did some simple gettimeofday timing of
"master" vs the fast-scale branch[1]. I say "master", because I actually
applied the branch to commit 94f58 since it doesn't apply to the later
version.

With commit 94f58:
Scaling from 640x480 to 1024x768 in 2013 usec

With commit 94f58 + fast-scale:
Scaling from 640x480 to 1024x768 in 709 usec

(These are the minimum frame scale times, which should give least error
from other random stuff happening on the machine.)

This clearly is a significant win, and I'd like to get this branch (or
something based on it) into 0.18.0 to avoid performance regressions in
spice.

[1] http://cgit.freedesktop.org/~siamashka/pixman/log/?h=fast-scaling

-- 
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 Alexander Larsson                                            Red Hat, Inc 
       alexl at redhat.com            alexander.larsson at gmail.com 
He's a hate-fuelled chivalrous vagrant with a secret. She's a strong-willed 
extravagent stripper with a song in her heart and a spring in her step. They 
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