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Cache loop filter errors.

This avoids fitlering a frame multiple times at the same level.

Change-Id: I1fd54dd7ea257d16da8569f48036b8fad3a3ed61

--- a/vp9/encoder/vp9_picklpf.c

+++ b/vp9/encoder/vp9_picklpf.c

@@ -64,16 +64,23 @@

   // range.

   int filt_mid = clamp(lf->filter_level, min_filter_level, max_filter_level);

   int filter_step = filt_mid < 16 ? 4 : filt_mid / 4;

+  // Sum squared error at each filter level

+  int ss_err[MAX_LOOP_FILTER + 1];

+  // Set each entry to -1

+  vpx_memset(ss_err, 0xFF, sizeof(ss_err));

+

   //  Make a copy of the unfiltered / processed recon buffer

   vpx_yv12_copy_y(cm->frame_to_show, &cpi->last_frame_uf);

   best_err = try_filter_frame(sd, cpi, xd, cm, filt_mid, partial);

   filt_best = filt_mid;

+  ss_err[filt_mid] = best_err;

   while (filter_step > 0) {

     const int filt_high = MIN(filt_mid + filter_step, max_filter_level);

     const int filt_low = MAX(filt_mid - filter_step, min_filter_level);

+    int filt_err;

     // Bias against raising loop filter in favor of lowering it.

     int bias = (best_err >> (15 - (filt_mid / 8))) * filter_step;

@@ -87,7 +94,12 @@

     if (filt_direction <= 0 && filt_low != filt_mid) {

       // Get Low filter error score

-      int filt_err = try_filter_frame(sd, cpi, xd, cm, filt_low, partial);

+      if (ss_err[filt_low] < 0) {

+        filt_err = try_filter_frame(sd, cpi, xd, cm, filt_low, partial);

+        ss_err[filt_low] = filt_err;

+      } else {

+        filt_err = ss_err[filt_low];

+      }

       // If value is close to the best so far then bias towards a lower loop

       // filter value.

       if ((filt_err - bias) < best_err) {

@@ -101,7 +113,12 @@

     // Now look at filt_high

     if (filt_direction >= 0 && filt_high != filt_mid) {

-      int filt_err = try_filter_frame(sd, cpi, xd, cm, filt_high, partial);

+      if (ss_err[filt_high] < 0) {

+        filt_err = try_filter_frame(sd, cpi, xd, cm, filt_high, partial);

+        ss_err[filt_high] = filt_err;

+      } else {

+        filt_err = ss_err[filt_high];

+      }

       // Was it better than the previous best?

       if (filt_err < (best_err - bias)) {

         best_err = filt_err;