shithub: libvpx

Info  •  Files  •  Log  •  Branches

Change log2_fast to log2_approximation

This reduce non_greedy_mv encoding time by 8.9%

Use linear approximation for value >= 1024

BDRate increases slightly on hdres
lowres: -0.002
midres: 0.007
hdres: 0.057

Change-Id: I55fd5e0bf0ab2206a286e11974f701cc48084be8

--- a/vp9/encoder/vp9_mcomp.c

+++ b/vp9/encoder/vp9_mcomp.c

@@ -1884,12 +1884,15 @@

   9.998590,

 };

-static double log2_fast(int v) {

+static double log2_approximation(int v) {

   assert(v > 0);

   if (v < LOG2_TABLE_SIZE) {

     return log2_table[v];

   } else {

-    return log2(v);

+    // use linear approximation when v >= 2^10

+    const double slope = 0.001409;  // slope = 1 / (log(2) * 1024)

+    assert(LOG2_TABLE_SIZE == 1 << 10);

+    return slope * (v - LOG2_TABLE_SIZE) + 10;

   }

 }

 double vp9_nb_mvs_inconsistency(const MV *mv, const int_mv *nb_mvs,

@@ -1903,7 +1906,8 @@

       MV nb_mv = nb_mvs[i].as_mv;

       const int row_diff = abs(mv->row - nb_mv.row);

       const int col_diff = abs(mv->col - nb_mv.col);

-      double cost = log2_fast(1 + row_diff * row_diff + col_diff * col_diff);

+      double cost =

+          log2_approximation(1 + row_diff * row_diff + col_diff * col_diff);

       if (update == 0) {

         best_cost = cost;

         update = 1;