shithub: libvpx

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Replace division with bit shift in choose_partitioning

This commit explicitly uses the bit shift operation instead of
division for computing block variance.

Change-Id: Id19c0ff27dd1d1ae4aceee6657e1aad0d406bd74

--- a/vp9/encoder/vp9_encodeframe.c

+++ b/vp9/encoder/vp9_encodeframe.c

@@ -278,7 +278,7 @@

 typedef struct {

   int64_t sum_square_error;

   int64_t sum_error;

-  int count;

+  int log2_count;

   int variance;

 } var;

@@ -374,21 +374,18 @@

 static void fill_variance(int64_t s2, int64_t s, int c, var *v) {

   v->sum_square_error = s2;

   v->sum_error = s;

-  v->count = c;

+  v->log2_count = c;

 }

 static void get_variance(var *v) {

-  if (v->count > 0)

-    v->variance = (int)(256 *

-                        (v->sum_square_error - v->sum_error * v->sum_error /

-                         v->count) / v->count);

-  else

-    v->variance = 0;

+  v->variance = (int)(256 * (v->sum_square_error -

+      ((v->sum_error * v->sum_error) >> v->log2_count)) >> v->log2_count);

 }

 void sum_2_variances(const var *a, const var *b, var *r) {

+  assert(a->log2_count == b->log2_count);

   fill_variance(a->sum_square_error + b->sum_square_error,

-                a->sum_error + b->sum_error, a->count + b->count, r);

+                a->sum_error + b->sum_error, a->log2_count + 1, r);

 }

 static void fill_variance_tree(void *data, BLOCK_SIZE bsize) {

@@ -585,7 +582,7 @@

           // If variance is based on 8x8 downsampling, we stop here and have

           // one sample for 8x8 block (so use 1 for count in fill_variance),

           // which of course means variance = 0 for 8x8 block.

-          fill_variance(sse, sum, 1, &vst->split[k].part_variances.none);

+          fill_variance(sse, sum, 0, &vst->split[k].part_variances.none);

         } else {

           // For key frame, go down to 4x4.

           v8x8 *vst2 = &vst->split[k];

@@ -603,7 +600,7 @@

             // If variance is based on 4x4 downsampling, we stop here and have

             // one sample for 4x4 block (so use 1 for count in fill_variance),

             // which of course means variance = 0 for 4x4 block.

-           fill_variance(sse, sum, 1, &vst2->split[m].part_variances.none);

+           fill_variance(sse, sum, 0, &vst2->split[m].part_variances.none);

           }

         }

       }