From d96fe5e079999587be7f0c73a528c69245adbee0 Mon Sep 17 00:00:00 2001
From: Pascal Massimino <pascal.massimino@gmail.com>
Date: Wed, 30 Mar 2016 23:18:54 -0700
Subject: [PATCH] WebPDequantizeLevels(): use stride in CountLevels()

follow-up for patch #333712

Change-Id: I3f85e3fce9e1c9d1a862a14ba56134882807718f
---
 src/dec/alpha.c              | 22 ++++++++++------------
 src/utils/quant_levels_dec.c | 21 ++++++++++++---------
 2 files changed, 22 insertions(+), 21 deletions(-)

diff --git a/src/dec/alpha.c b/src/dec/alpha.c
index 6d54b92a..7f90ddca 100644
--- a/src/dec/alpha.c
+++ b/src/dec/alpha.c
@@ -122,12 +122,12 @@ static int ALPHDecode(VP8Decoder* const dec, int row, int num_rows) {
 const uint8_t* VP8DecompressAlphaRows(VP8Decoder* const dec,
                                       const VP8Io* const io,
                                       int row, int num_rows) {
-  const int width = dec->pic_hdr_.width_;
-  const int height = dec->pic_hdr_.height_;
+  const int width = io->width;
+  const int height = io->crop_bottom;
 
   assert(dec != NULL && io != NULL);
 
-  if (row < 0 || num_rows <= 0 || row + num_rows > height) {
+  if (row < 0 || num_rows <= 0 || row + num_rows > io->height) {
     return NULL;    // sanity check.
   }
 
@@ -136,7 +136,7 @@ const uint8_t* VP8DecompressAlphaRows(VP8Decoder* const dec,
     dec->alph_dec_ = ALPHNew();
     if (dec->alph_dec_ == NULL) return NULL;
     if (!ALPHInit(dec->alph_dec_, dec->alpha_data_, dec->alpha_data_size_,
-                  width, height, dec->alpha_plane_)) {
+                  io->width, io->height, dec->alpha_plane_)) {
       ALPHDelete(dec->alph_dec_);
       dec->alph_dec_ = NULL;
       return NULL;
@@ -149,23 +149,21 @@ const uint8_t* VP8DecompressAlphaRows(VP8Decoder* const dec,
     }
   }
 
-  if (io->use_cropping) {
-    if (row + num_rows > io->crop_bottom) {
-      num_rows = io->crop_bottom - row;
-    }
+  if (row + num_rows > height) {
+    num_rows = height - row;
   }
 
   if (!dec->is_alpha_decoded_) {
     int ok = ALPHDecode(dec, row, num_rows);
     assert(dec->alph_dec_ != NULL);
-    if (ok && dec->alpha_dithering_ > 0) {
-      ok = WebPDequantizeLevels(dec->alpha_plane_, width, height, width,
-                                dec->alpha_dithering_);
-    }
     if (!ok || dec->is_alpha_decoded_) {
       ALPHDelete(dec->alph_dec_);
       dec->alph_dec_ = NULL;
     }
+    if (ok && dec->is_alpha_decoded_ && dec->alpha_dithering_ > 0) {
+      ok = WebPDequantizeLevels(dec->alpha_plane_, width, height, width,
+                                dec->alpha_dithering_);
+    }
     if (!ok) return NULL;  // Error.
   }
   // Return a pointer to the current decoded row.
diff --git a/src/utils/quant_levels_dec.c b/src/utils/quant_levels_dec.c
index 05b42616..ee0a3fe1 100644
--- a/src/utils/quant_levels_dec.c
+++ b/src/utils/quant_levels_dec.c
@@ -179,17 +179,20 @@ static void InitCorrectionLUT(int16_t* const lut, int min_dist) {
   lut[0] = 0;
 }
 
-static void CountLevels(const uint8_t* const data, int size,
-                        SmoothParams* const p) {
-  int i, last_level;
+static void CountLevels(SmoothParams* const p) {
+  int i, j, last_level;
   uint8_t used_levels[256] = { 0 };
+  const uint8_t* data = p->src_;
   p->min_ = 255;
   p->max_ = 0;
-  for (i = 0; i < size; ++i) {
-    const int v = data[i];
-    if (v < p->min_) p->min_ = v;
-    if (v > p->max_) p->max_ = v;
-    used_levels[v] = 1;
+  for (j = 0; j < p->height_; ++j) {
+    for (i = 0; i < p->width_; ++i) {
+      const int v = data[i];
+      if (v < p->min_) p->min_ = v;
+      if (v > p->max_) p->max_ = v;
+      used_levels[v] = 1;
+    }
+    data += p->stride_;
   }
   // Compute the mininum distance between two non-zero levels.
   p->min_level_dist_ = p->max_ - p->min_;
@@ -242,7 +245,7 @@ static int InitParams(uint8_t* const data, int width, int height, int stride,
   p->row_ = -radius;
 
   // analyze the input distribution so we can best-fit the threshold
-  CountLevels(data, width * height, p);
+  CountLevels(p);
 
   // correction table
   p->correction_ = ((int16_t*)mem) + LUT_SIZE;