[FFmpeg-devel] [PATCH] faster vp6 decoding

[Jason Garrett-Glaser]

+    "punpcklbw %%mm7, %%mm0\n\t"                                \
+    "punpcklbw %%mm7, %%mm1\n\t"                                \
+    "punpckhbw %%mm7, %%mm3\n\t"                                \
+    "punpckhbw %%mm7, %%mm4\n\t"                                \
+    "pmullw  0(%2), %%mm0\n\t" /* src[x-8 ] * biweight [0] */   \
+    "pmullw  8(%2), %%mm1\n\t" /* src[x   ] * biweight [1] */   \
+    "pmullw  0(%2), %%mm3\n\t" /* src[x-8 ] * biweight [0] */   \
+    "pmullw  8(%2), %%mm4\n\t" /* src[x   ] * biweight [1] */   \
+    "paddw %%mm1, %%mm0\n\t"                                    \
+    "paddw %%mm4, %%mm3\n\t"                                    \

This can be done faster with pmaddubsw (SSSE3-only, but worth making
another version surely).  Worthwhile if you make an SSE version.
Works by interleaving the weights, allowing you to avoid the unpacks,
use only two multiplies, and avoid the adds, too, I think.  If I'm
right, that makes the entire thing quite a bit less than half the
instructions.

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