From f4059d0c7d5627c6baef0472c6978e4358e64ebf Mon Sep 17 00:00:00 2001
From: Vikas Arora <vikasa@google.com>
Date: Tue, 26 Aug 2014 15:44:04 -0700
Subject: [PATCH] Code cleanup for HistogramRemap.

Avoid call to HistogramAddThresh when there's only one Histogram image.
Change-Id: I43b09e8e2d218c95969567034224777dcce37ab9
---
 src/enc/histogram.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/enc/histogram.c b/src/enc/histogram.c
index 7c6abb4d..79879b32 100644
--- a/src/enc/histogram.c
+++ b/src/enc/histogram.c
@@ -640,12 +640,15 @@ static void HistogramRemap(const VP8LHistogramSet* const orig_histo,
   int i;
   VP8LHistogram** const orig_histograms = orig_histo->histograms;
   VP8LHistogram** const histograms = image_histo->histograms;
-  for (i = 0; i < orig_histo->size; ++i) {
+  const int orig_histo_size = orig_histo->size;
+  const int image_histo_size = image_histo->size;
+  if (image_histo_size > 1) {
+    for (i = 0; i < orig_histo_size; ++i) {
     int best_out = 0;
     double best_bits =
         HistogramAddThresh(histograms[0], orig_histograms[i], MAX_COST);
     int k;
-    for (k = 1; k < image_histo->size; ++k) {
+      for (k = 1; k < image_histo_size; ++k) {
       const double cur_bits =
           HistogramAddThresh(histograms[k], orig_histograms[i], best_bits);
       if (cur_bits < best_bits) {
@@ -655,13 +658,19 @@ static void HistogramRemap(const VP8LHistogramSet* const orig_histo,
     }
     symbols[i] = best_out;
   }
+  } else {
+    assert(image_histo_size == 1);
+    for (i = 0; i < orig_histo_size; ++i) {
+      symbols[i] = 0;
+    }
+  }
 
   // Recompute each out based on raw and symbols.
-  for (i = 0; i < image_histo->size; ++i) {
+  for (i = 0; i < image_histo_size; ++i) {
     HistogramClear(histograms[i]);
   }
 
-  for (i = 0; i < orig_histo->size; ++i) {
+  for (i = 0; i < orig_histo_size; ++i) {
     const int idx = symbols[i];
     VP8LHistogramAdd(orig_histograms[i], histograms[idx], histograms[idx]);
   }