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vp9_reconintra: simplify d63_predictor

calculate the averages needed for even and odd rows once; this removes a
conditional from the inner loop
the final average calculated currently relies on above[] being extended,
it could be reduced to use
above[block_size - 2] + 3 * above[block_size - 1]

Change-Id: I70f5eac8d8a2a959c7114844a95826f445c3dd4d

--- a/vp9/common/vp9_reconintra.c

+++ b/vp9/common/vp9_reconintra.c

@@ -425,13 +425,17 @@

 static INLINE void d63_predictor(uint8_t *dst, ptrdiff_t stride, int bs,

                                  const uint8_t *above, const uint8_t *left) {

   int r, c;

-  (void) left;

-  for (r = 0; r < bs; ++r) {

-    for (c = 0; c < bs; ++c)

-      dst[c] = r & 1 ? AVG3(above[(r >> 1) + c], above[(r >> 1) + c + 1],

-                            above[(r >> 1) + c + 2])

-                     : AVG2(above[(r >> 1) + c], above[(r >> 1) + c + 1]);

-    dst += stride;

+  int size;

+  (void)left;

+  for (c = 0; c < bs; ++c) {

+    dst[c] = AVG2(above[c], above[c + 1]);

+    dst[stride + c] = AVG3(above[c], above[c + 1], above[c + 2]);

+  }

+  for (r = 2, size = bs - 2; r < bs; r += 2, --size) {

+    memcpy(dst + (r + 0) * stride, dst + (r >> 1), size);

+    memset(dst + (r + 0) * stride + size, above[bs - 1], bs - size);

+    memcpy(dst + (r + 1) * stride, dst + stride + (r >> 1), size);

+    memset(dst + (r + 1) * stride + size, above[bs - 1], bs - size);

   }

 }

 intra_pred_no_4x4(d63)