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vp9_reconintra: simplify d45_predictor

only the immediate above right pixel is needed; 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_right

Change-Id: Ica4f2b8d25eec3ca1d6fa52ef0d4adc228eeea3f

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

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

@@ -430,14 +430,17 @@

 static INLINE void d45_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 + c + 2 < bs * 2 ?  ROUND_POWER_OF_TWO(above[r + c] +

-                                                        above[r + c + 1] * 2 +

-                                                        above[r + c + 2], 2)

-                                  : above[bs * 2 - 1];

+  const uint8_t above_right = above[bs - 1];

+  int x, size;

+  uint8_t avg[31];  // TODO(jzern): this could be block size specific

+  (void)left;

+

+  for (x = 0; x < bs - 1; ++x) {

+    avg[x] = AVG3(above[x], above[x + 1], above[x + 2]);

+  }

+  for (x = 0, size = bs - 1; x < bs; ++x, --size) {

+    memcpy(dst, avg + x, size);

+    memset(dst + size, above_right, x + 1);

     dst += stride;

   }

 }

-- 

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