From b30a04cf119db3a6dca4f5c97d45d2dc1cd713c8 Mon Sep 17 00:00:00 2001
From: skal <pascal.massimino@gmail.com>
Date: Mon, 14 Apr 2014 17:57:26 +0200
Subject: [PATCH] WIP: extract the float-calculation of HuffmanCost from loop

new function: VP8FinalHuffmanCost()

Change-Id: I42102f8e5ef6d7a7af66490af77b7dc2048a9cb9
---
 src/enc/histogram.c | 59 ++++++++++++++++++++++++---------------------
 src/enc/histogram.h |  7 ++++++
 2 files changed, 39 insertions(+), 27 deletions(-)

diff --git a/src/enc/histogram.c b/src/enc/histogram.c
index 39a12e49..82048677 100644
--- a/src/enc/histogram.c
+++ b/src/enc/histogram.c
@@ -188,59 +188,64 @@ static WEBP_INLINE double InitialHuffmanCost(void) {
   return kHuffmanCodeOfHuffmanCodeSize - kSmallBias;
 }
 
-static WEBP_INLINE double HuffmanCostRefine(int streak, int val) {
-  double retval;
-  if (streak > 3) {
-    if (val == 0) {
-      retval = 1.5625 + 0.234375 * streak;
-    } else {
-      retval = 2.578125 + 0.703125 * streak;
-    }
-  } else {
-    if (val == 0) {
-      retval = 1.796875 * streak;
-    } else {
-      retval = 3.28125 * streak;
-    }
-  }
+double VP8FinalHuffmanCost(int cnt_z, int streak_z_le3, int streak_z_gt3,
+                           int cnt_nz, int streak_nz_le3, int streak_nz_gt3) {
+  double retval = InitialHuffmanCost();
+  retval += cnt_z * 1.5625 + 0.234375 * streak_z_gt3;
+  retval += cnt_nz * 2.578125 + 0.703125 * streak_nz_gt3;
+  retval += 1.796875 * streak_z_le3;
+  retval += 3.28125 * streak_nz_le3;
   return retval;
 }
 
 // Returns the cost encode the rle-encoded entropy code.
 // The constants in this function are experimental.
 static double HuffmanCost(const int* const population, int length) {
+  int cnts[2] = { 0, 0 };
+  int streaks[2][2] = { { 0, 0 }, { 0, 0 } };
   int streak = 0;
-  int i = 0;
-  double retval = InitialHuffmanCost();
-  for (; i < length - 1; ++i) {
+  int i;
+  for (i = 0; i < length - 1; ++i) {
     ++streak;
     if (population[i] == population[i + 1]) {
       continue;
     }
-    retval += HuffmanCostRefine(streak, population[i]);
+    cnts[population[i] != 0] += (streak > 3);
+    streaks[population[i] != 0][(streak > 3)] += streak;
     streak = 0;
   }
-  retval += HuffmanCostRefine(++streak, population[i]);
-  return retval;
+  ++streak;
+  cnts[population[i] != 0] += (streak > 3);
+  streaks[population[i] != 0][(streak > 3)] += streak;
+  return VP8FinalHuffmanCost(cnts[0], streaks[0][0], streaks[0][1],
+                             cnts[1], streaks[1][0], streaks[1][1]);
 }
 
 static double HuffmanCostCombined(const int* const X, const int* const Y,
                                   int length) {
+  int cnts[2] = { 0, 0 };
+  int streaks[2][2] = { { 0, 0 }, { 0, 0 } };
   int streak = 0;
-  int i = 0;
-  double retval = InitialHuffmanCost();
-  for (; i < length - 1; ++i) {
+  int i;
+  for (i = 0; i < length - 1; ++i) {
     const int xy = X[i] + Y[i];
     const int xy_next = X[i + 1] + Y[i + 1];
     ++streak;
     if (xy == xy_next) {
       continue;
     }
-    retval += HuffmanCostRefine(streak, xy);
+    cnts[xy != 0] += (streak > 3);
+    streaks[xy != 0][streak > 3] += streak;
     streak = 0;
   }
-  retval += HuffmanCostRefine(++streak, X[i] + Y[i]);
-  return retval;
+  {
+    const int xy = X[i] + Y[i];
+    ++streak;
+    cnts[xy != 0] += (streak > 3);
+    streaks[xy != 0][streak > 3] += streak;
+  }
+  return VP8FinalHuffmanCost(cnts[0], streaks[0][0], streaks[0][1],
+                             cnts[1], streaks[1][0], streaks[1][1]);
 }
 
 static double PopulationCost(const int* const population, int length) {
diff --git a/src/enc/histogram.h b/src/enc/histogram.h
index 9d13ecd5..e8c3b9d1 100644
--- a/src/enc/histogram.h
+++ b/src/enc/histogram.h
@@ -90,6 +90,13 @@ static WEBP_INLINE int VP8LHistogramNumCodes(int palette_code_bits) {
       ((palette_code_bits > 0) ? (1 << palette_code_bits) : 0);
 }
 
+// Used to finalized the Huffman cost:
+// cnt_z / cnt_nz: counts the number of 0's and non-0's
+// streak_{z,nz}_le3 / streak_{z,nz}_gt3: number of streaks larger than 3
+// or less-or-equal than 3.
+double VP8FinalHuffmanCost(int cnt_z, int streak_z_le3, int streak_z_gt3,
+                           int cnt_nz, int streak_nz_le3, int streak_nz_gt3);
+
 // Builds the histogram image.
 int VP8LGetHistoImageSymbols(int xsize, int ysize,
                              const VP8LBackwardRefs* const refs,