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authorRoland Scheidegger <[email protected]>2010-09-24 15:17:07 +0200
committerJosé Fonseca <[email protected]>2010-09-25 12:19:31 +0100
commit049a8cce76b1148ab00de1ae207171e519bfafca (patch)
tree2dc7640c23c22be517ee1e2d60714733ade41bc5 /scons
parent46d05d4ef99857e50d978247917f3e16574418f4 (diff)
gallivm: optimize yuv decoding
this is more a proof to show vector shifts on x86 with per-element shift count are evil. Since we can avoid the shift with a single compare/select, use that instead. Replaces more than 20 instructions (and slow ones at that) with about 3, and cuts compiled shader size with mesa's yuvsqure demo by over 10% (no performance measurements done - but selection is blazing fast). Might want to revisit that for future cpus - unfortunately AVX won't have vector shifts neither, but AMD's XOP will, but even in that case using selection here is probably not slower.
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