shithub: libvpx

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Merge "Add dynamic range notes to vp9_vector_var_c"

--- a/vp9/encoder/vp9_avg.c

+++ b/vp9/encoder/vp9_avg.c

@@ -155,6 +155,9 @@

   return sum;

 }

+// ref: [0 - 510]

+// src: [0 - 510]

+// bwl: {2, 3, 4}

 int vp9_vector_var_c(int16_t const *ref, int16_t const *src,

                      const int bwl) {

   int i;

@@ -162,11 +165,12 @@

   int sse = 0, mean = 0, var;

   for (i = 0; i < width; ++i) {

-    int diff = ref[i] - src[i];

-    mean += diff;

-    sse += diff * diff;

+    int diff = ref[i] - src[i];  // diff: dynamic range [-510, 510], 10 bits.

+    mean += diff;                // mean: dynamic range 16 bits.

+    sse += diff * diff;          // sse:  dynamic range 26 bits.

   }

+  // (mean * mean): dynamic range 31 bits.

   var = sse - ((mean * mean) >> (bwl + 2));

   return var;

 }