Convert LZW decompressor to use vector instead of static arraychromium/3230chromium/3229chromium/3228chromium/3227

Speciifically replacing what was called the "stack_", an array, with a
vector called "decompressed_". The fact that this data structure
wasn't actually a stack caused a lot of grief when refactoring.

BUG=pdfium:903

Change-Id: I056f8fc9183bcde67a03dc9de0dae9ddf9fb0f37
Reviewed-on: https://pdfium-review.googlesource.com/15092
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: Ryan Harrison <rharrison@chromium.org>

3 files changed, 177 insertions, 86 deletions

diff --git a/core/fxcodec/gif/cfx_lzwdecompressor.cpp b/core/fxcodec/gif/cfx_lzwdecompressor.cpp
index 27e36b12e9..1ee7b5a217 100644
--- a/core/fxcodec/gif/cfx_lzwdecompressor.cpp
+++ b/core/fxcodec/gif/cfx_lzwdecompressor.cpp
@@ -18,7 +18,9 @@
 std::unique_ptr<CFX_LZWDecompressor> CFX_LZWDecompressor::Create(
     uint8_t color_exp,
     uint8_t code_exp) {
-  if (code_exp > GIF_MAX_LZW_EXP || code_exp + 1 < color_exp)
+  // color_exp generates 2^(n + 1) codes, where as the code_exp reserves 2^n.
+  // This is a quirk of the GIF spec.
+  if (code_exp > GIF_MAX_LZW_EXP || code_exp < color_exp + 1)
     return nullptr;
   return std::unique_ptr<CFX_LZWDecompressor>(
       new CFX_LZWDecompressor(color_exp, code_exp));
@@ -27,12 +29,11 @@ std::unique_ptr<CFX_LZWDecompressor> CFX_LZWDecompressor::Create(
 CFX_LZWDecompressor::CFX_LZWDecompressor(uint8_t color_exp, uint8_t code_exp)
     : code_size_(code_exp),
       code_size_cur_(0),
-      code_color_end_(static_cast<uint16_t>(2 << color_exp)),
+      code_color_end_(static_cast<uint16_t>(1 << (color_exp + 1))),
       code_clear_(static_cast<uint16_t>(1 << code_exp)),
       code_end_(static_cast<uint16_t>((1 << code_exp) + 1)),
       code_next_(0),
       code_first_(0),
-      stack_size_(0),
       code_old_(0),
       next_in_(nullptr),
       avail_in_(0),
@@ -57,17 +58,13 @@ CFX_GifDecodeStatus CFX_LZWDecompressor::Decode(uint8_t* src_buf,
   ClearTable();
 
   uint32_t i = 0;
-  if (stack_size_ != 0) {
-    if (*des_size < stack_size_) {
-      memcpy(des_buf, &stack_[GIF_MAX_LZW_CODE - stack_size_], *des_size);
-      stack_size_ -= static_cast<uint16_t>(*des_size);
+  if (decompressed_next_ != 0) {
+    uint32_t extracted_size = ExtractData(des_buf, *des_size);
+    if (decompressed_next_ != 0)
       return CFX_GifDecodeStatus::InsufficientDestSize;
-    }
 
-    memcpy(des_buf, &stack_[GIF_MAX_LZW_CODE - stack_size_], stack_size_);
-    des_buf += stack_size_;
-    i += stack_size_;
-    stack_size_ = 0;
+    des_buf += extracted_size;
+    i += extracted_size;
   }
 
   while (i <= *des_size && (avail_in_ > 0 || bits_left_ >= code_size_cur_)) {
@@ -115,7 +112,7 @@ CFX_GifDecodeStatus CFX_LZWDecompressor::Decode(uint8_t* src_buf,
             if (!DecodeString(code))
               return CFX_GifDecodeStatus::Error;
 
-            uint8_t append_char = stack_[GIF_MAX_LZW_CODE - stack_size_];
+            uint8_t append_char = decompressed_[decompressed_next_ - 1];
             AddCode(code_old_, append_char);
           }
         }
@@ -125,16 +122,12 @@ CFX_GifDecodeStatus CFX_LZWDecompressor::Decode(uint8_t* src_buf,
       }
 
       code_old_ = code;
-      if (i + stack_size_ > *des_size) {
-        memcpy(des_buf, &stack_[GIF_MAX_LZW_CODE - stack_size_], *des_size - i);
-        stack_size_ -= static_cast<uint16_t>(*des_size - i);
+      uint32_t extracted_size = ExtractData(des_buf, *des_size - i);
+      if (decompressed_next_ != 0)
         return CFX_GifDecodeStatus::InsufficientDestSize;
-      }
 
-      memcpy(des_buf, &stack_[GIF_MAX_LZW_CODE - stack_size_], stack_size_);
-      des_buf += stack_size_;
-      i += stack_size_;
-      stack_size_ = 0;
+      des_buf += extracted_size;
+      i += extracted_size;
     }
   }
 
@@ -150,9 +143,10 @@ void CFX_LZWDecompressor::ClearTable() {
   code_next_ = code_end_ + 1;
   code_old_ = static_cast<uint16_t>(-1);
   memset(code_table_, 0, sizeof(code_table_));
-  memset(stack_, 0, sizeof(stack_));
   for (uint16_t i = 0; i < code_clear_; i++)
     code_table_[i].suffix = static_cast<uint8_t>(i);
+  decompressed_.resize(code_next_ - code_clear_ + 1);
+  decompressed_next_ = 0;
 }
 
 void CFX_LZWDecompressor::AddCode(uint16_t prefix_code, uint8_t append_char) {
@@ -168,18 +162,35 @@ void CFX_LZWDecompressor::AddCode(uint16_t prefix_code, uint8_t append_char) {
 }
 
 bool CFX_LZWDecompressor::DecodeString(uint16_t code) {
-  stack_size_ = 0;
+  decompressed_.resize(code_next_ - code_clear_ + 1);
+  decompressed_next_ = 0;
+
   while (code >= code_clear_ && code <= code_next_) {
-    if (code == code_table_[code].prefix || stack_size_ == GIF_MAX_LZW_CODE - 1)
+    if (code == code_table_[code].prefix ||
+        decompressed_next_ >= decompressed_.size())
       return false;
 
-    stack_[GIF_MAX_LZW_CODE - 1 - stack_size_++] = code_table_[code].suffix;
+    decompressed_[decompressed_next_++] = code_table_[code].suffix;
     code = code_table_[code].prefix;
   }
+
   if (code >= code_color_end_)
     return false;
 
-  stack_[GIF_MAX_LZW_CODE - 1 - stack_size_++] = static_cast<uint8_t>(code);
+  decompressed_[decompressed_next_++] = static_cast<uint8_t>(code);
   code_first_ = static_cast<uint8_t>(code);
   return true;
 }
+
+uint32_t CFX_LZWDecompressor::ExtractData(uint8_t* des_buf, uint32_t des_size) {
+  if (des_size == 0)
+    return 0;
+
+  uint32_t copy_size = des_size <= decompressed_next_
+                           ? des_size
+                           : static_cast<uint32_t>(decompressed_next_);
+  std::reverse_copy(decompressed_.data() + decompressed_next_ - copy_size,
+                    decompressed_.data() + decompressed_next_, des_buf);
+  decompressed_next_ -= copy_size;
+  return copy_size;
+}
diff --git a/core/fxcodec/gif/cfx_lzwdecompressor.h b/core/fxcodec/gif/cfx_lzwdecompressor.h
index 10c0a566d7..717c055973 100644
--- a/core/fxcodec/gif/cfx_lzwdecompressor.h
+++ b/core/fxcodec/gif/cfx_lzwdecompressor.h
@@ -29,11 +29,21 @@ class CFX_LZWDecompressor {
                              uint8_t* des_buf,
                              uint32_t* des_size);
 
+  // Used by unittests, should not be called in production code.
+  uint32_t ExtractDataForTest(uint8_t* des_buf, uint32_t des_size) {
+    return ExtractData(des_buf, des_size);
+  }
+
+  std::vector<uint8_t>* DecompressedForTest() { return &decompressed_; }
+
+  size_t* DecompressedNextForTest() { return &decompressed_next_; }
+
  private:
   CFX_LZWDecompressor(uint8_t color_exp, uint8_t code_exp);
   void ClearTable();
   void AddCode(uint16_t prefix_code, uint8_t append_char);
   bool DecodeString(uint16_t code);
+  uint32_t ExtractData(uint8_t* des_buf, uint32_t des_size);
 
   uint8_t code_size_;
   uint8_t code_size_cur_;
@@ -42,8 +52,8 @@ class CFX_LZWDecompressor {
   uint16_t code_end_;
   uint16_t code_next_;
   uint8_t code_first_;
-  uint8_t stack_[GIF_MAX_LZW_CODE];
-  size_t stack_size_;
+  std::vector<uint8_t> decompressed_;
+  size_t decompressed_next_;
   CodeEntry code_table_[GIF_MAX_LZW_CODE];
   uint16_t code_old_;
   uint8_t* next_in_;
diff --git a/core/fxcodec/gif/cfx_lzwdecompressor_unittest.cpp b/core/fxcodec/gif/cfx_lzwdecompressor_unittest.cpp
index cc3ce6367d..0d0906eb10 100644
--- a/core/fxcodec/gif/cfx_lzwdecompressor_unittest.cpp
+++ b/core/fxcodec/gif/cfx_lzwdecompressor_unittest.cpp
@@ -8,16 +8,79 @@
 #include "testing/gtest/include/gtest/gtest.h"
 
 TEST(CFX_LZWDecompressor, CreateBadParams) {
-  EXPECT_EQ(nullptr, CFX_LZWDecompressor::Create(0x10, 0x2));
-  EXPECT_EQ(nullptr, CFX_LZWDecompressor::Create(0x4, 0x0F));
+  EXPECT_EQ(nullptr, CFX_LZWDecompressor::Create(0x10, 0x02));
+  EXPECT_EQ(nullptr, CFX_LZWDecompressor::Create(0x04, 0x0F));
+  EXPECT_EQ(nullptr, CFX_LZWDecompressor::Create(0x02, 0x02));
+}
+
+TEST(CFX_LZWDecompressor, ExtractData) {
+  uint8_t palette_exp = 0x1;
+  uint8_t code_exp = 0x2;
+  auto decompressor = CFX_LZWDecompressor::Create(palette_exp, code_exp);
+  ASSERT_NE(nullptr, decompressor);
+
+  // Check that 0 length extract does nothing
+  {
+    std::vector<uint8_t>* decompressed = decompressor->DecompressedForTest();
+    *decompressed = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
+    *(decompressor->DecompressedNextForTest()) = decompressed->size();
+    uint8_t des_buf[20];
+    memset(des_buf, static_cast<uint8_t>(-1), sizeof(des_buf));
+
+    EXPECT_EQ(0u, decompressor->ExtractDataForTest(des_buf, 0));
+    for (size_t i = 0; i < FX_ArraySize(des_buf); ++i)
+      EXPECT_EQ(static_cast<uint8_t>(-1), des_buf[i]);
+
+    EXPECT_EQ(10u, *(decompressor->DecompressedNextForTest()));
+    for (size_t i = 0; i < *(decompressor->DecompressedNextForTest()); ++i)
+      EXPECT_EQ(i, decompressed->operator[](i));
+  }
+
+  // Check that less than decompressed size only gets the expected number
+  {
+    std::vector<uint8_t>* decompressed = decompressor->DecompressedForTest();
+    *decompressed = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
+    *(decompressor->DecompressedNextForTest()) = decompressed->size();
+    uint8_t des_buf[20];
+    memset(des_buf, static_cast<uint8_t>(-1), sizeof(des_buf));
+
+    EXPECT_EQ(5u, decompressor->ExtractDataForTest(des_buf, 5));
+    size_t i = 0;
+    for (; i < 5; ++i)
+      EXPECT_EQ(9 - i, des_buf[i]);
+    for (; i < FX_ArraySize(des_buf); ++i)
+      EXPECT_EQ(static_cast<uint8_t>(-1), des_buf[i]);
+
+    EXPECT_EQ(5u, *(decompressor->DecompressedNextForTest()));
+    for (i = 0; i < *(decompressor->DecompressedNextForTest()); ++i)
+      EXPECT_EQ(i, decompressed->operator[](i));
+  }
+
+  // Check that greater than decompressed size depletes the decompressor
+  {
+    std::vector<uint8_t>* decompressed = decompressor->DecompressedForTest();
+    *decompressed = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
+    *(decompressor->DecompressedNextForTest()) = decompressed->size();
+    uint8_t des_buf[20];
+    memset(des_buf, static_cast<uint8_t>(-1), sizeof(des_buf));
+
+    EXPECT_EQ(10u,
+              decompressor->ExtractDataForTest(des_buf, FX_ArraySize(des_buf)));
+    size_t i = 0;
+    for (; i < 10; ++i)
+      EXPECT_EQ(9 - i, des_buf[i]);
+    for (; i < FX_ArraySize(des_buf); ++i)
+      EXPECT_EQ(static_cast<uint8_t>(-1), des_buf[i]);
+
+    EXPECT_EQ(0u, *(decompressor->DecompressedNextForTest()));
+  }
 }
 
 TEST(CFX_LZWDecompressor, DecodeBadParams) {
   uint8_t palette_exp = 0x0;
   uint8_t code_exp = 0x2;
-
-  auto decoder = CFX_LZWDecompressor::Create(palette_exp, code_exp);
-  ASSERT_NE(nullptr, decoder);
+  auto decompressor = CFX_LZWDecompressor::Create(palette_exp, code_exp);
+  ASSERT_NE(nullptr, decompressor);
 
   uint8_t image_data[10];
   uint32_t image_size = FX_ArraySize(image_data);
@@ -25,36 +88,40 @@ TEST(CFX_LZWDecompressor, DecodeBadParams) {
   uint8_t output_data[10];
   uint32_t output_size = FX_ArraySize(output_data);
 
+  EXPECT_EQ(
+      CFX_GifDecodeStatus::Error,
+      decompressor->Decode(nullptr, image_size, output_data, &output_size));
   EXPECT_EQ(CFX_GifDecodeStatus::Error,
-            decoder->Decode(nullptr, image_size, output_data, &output_size));
+            decompressor->Decode(image_data, 0, output_data, &output_size));
+  EXPECT_EQ(
+      CFX_GifDecodeStatus::Error,
+      decompressor->Decode(image_data, image_size, nullptr, &output_size));
   EXPECT_EQ(CFX_GifDecodeStatus::Error,
-            decoder->Decode(image_data, 0, output_data, &output_size));
-  EXPECT_EQ(CFX_GifDecodeStatus::Error,
-            decoder->Decode(image_data, image_size, nullptr, &output_size));
-  EXPECT_EQ(CFX_GifDecodeStatus::Error,
-            decoder->Decode(image_data, image_size, output_data, nullptr));
+            decompressor->Decode(image_data, image_size, output_data, nullptr));
 
   output_size = 0;
-  EXPECT_EQ(CFX_GifDecodeStatus::InsufficientDestSize,
-            decoder->Decode(image_data, image_size, output_data, &output_size));
+  EXPECT_EQ(
+      CFX_GifDecodeStatus::InsufficientDestSize,
+      decompressor->Decode(image_data, image_size, output_data, &output_size));
 }
 
 TEST(CFX_LZWDecompressor, Decode1x1SingleColour) {
   uint8_t palette_exp = 0x0;
   uint8_t code_exp = 0x2;
-
-  auto decoder = CFX_LZWDecompressor::Create(palette_exp, code_exp);
-  ASSERT_NE(nullptr, decoder);
+  auto decompressor = CFX_LZWDecompressor::Create(palette_exp, code_exp);
+  ASSERT_NE(nullptr, decompressor);
 
   uint8_t image_data[] = {0x44, 0x01};
   uint32_t image_size = FX_ArraySize(image_data);
 
-  uint8_t output_data[1];
+  uint8_t expected_data[] = {0x00};
+  uint8_t output_data[FX_ArraySize(expected_data)];
+  memset(output_data, 0, sizeof(output_data));
   uint32_t output_size = FX_ArraySize(output_data);
 
-  EXPECT_EQ(CFX_GifDecodeStatus::Success,
-            decoder->Decode(image_data, image_size, output_data, &output_size));
-  uint8_t expected_data[] = {0x00};
+  EXPECT_EQ(
+      CFX_GifDecodeStatus::Success,
+      decompressor->Decode(image_data, image_size, output_data, &output_size));
 
   EXPECT_EQ(FX_ArraySize(output_data), output_size);
   EXPECT_TRUE(0 == memcmp(expected_data, output_data, sizeof(expected_data)));
@@ -63,29 +130,30 @@ TEST(CFX_LZWDecompressor, Decode1x1SingleColour) {
 TEST(CFX_LZWDecompressor, Decode10x10SingleColour) {
   uint8_t palette_exp = 0x0;
   uint8_t code_exp = 0x2;
-
-  auto decoder = CFX_LZWDecompressor::Create(palette_exp, code_exp);
-  ASSERT_NE(nullptr, decoder);
+  auto decompressor = CFX_LZWDecompressor::Create(palette_exp, code_exp);
+  ASSERT_NE(nullptr, decompressor);
 
   uint8_t image_data[] = {0x84, 0x8F, 0xA9, 0xCB, 0xED, 0x0F, 0x63, 0x2B};
   uint32_t image_size = FX_ArraySize(image_data);
 
-  uint8_t output_data[100];
+  uint8_t expected_data[] = {
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+  uint8_t output_data[FX_ArraySize(expected_data)];
   memset(output_data, 0, sizeof(output_data));
   uint32_t output_size = FX_ArraySize(output_data);
 
-  EXPECT_EQ(CFX_GifDecodeStatus::Success,
-            decoder->Decode(image_data, image_size, output_data, &output_size));
-  uint8_t expected_data[] = {
-      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
-      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
-      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
-      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
-      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
-      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
-      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
-      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
-      0x00, 0x00, 0x00, 0x00};
+  EXPECT_EQ(
+      CFX_GifDecodeStatus::Success,
+      decompressor->Decode(image_data, image_size, output_data, &output_size));
 
   EXPECT_EQ(FX_ArraySize(output_data), output_size);
   EXPECT_TRUE(0 == memcmp(expected_data, output_data, sizeof(expected_data)));
@@ -94,31 +162,33 @@ TEST(CFX_LZWDecompressor, Decode10x10SingleColour) {
 TEST(CFX_LZWDecompressor, Decode10x10MultipleColour) {
   uint8_t palette_exp = 0x1;
   uint8_t code_exp = 0x2;
-
-  auto decoder = CFX_LZWDecompressor::Create(palette_exp, code_exp);
-  ASSERT_NE(nullptr, decoder);
+  auto decompressor = CFX_LZWDecompressor::Create(palette_exp, code_exp);
+  ASSERT_NE(nullptr, decompressor);
 
   uint8_t image_data[] = {0x8C, 0x2D, 0x99, 0x87, 0x2A, 0x1C, 0xDC, 0x33,
                           0xA0, 0x02, 0x75, 0xEC, 0x95, 0xFA, 0xA8, 0xDE,
                           0x60, 0x8C, 0x04, 0x91, 0x4C, 0x01};
   uint32_t image_size = FX_ArraySize(image_data);
 
-  uint8_t output_data[100];
+  uint8_t expected_data[] = {
+    0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x02, 0x02, 0x02, 0x02,
+    0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x02, 0x02, 0x02, 0x02,
+    0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x02, 0x02, 0x02, 0x02,
+    0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x02, 0x02, 0x02,
+    0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x02, 0x02, 0x02,
+    0x02, 0x02, 0x02, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01, 0x01,
+    0x02, 0x02, 0x02, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01, 0x01,
+    0x02, 0x02, 0x02, 0x02, 0x02, 0x01, 0x01, 0x01, 0x01, 0x01,
+    0x02, 0x02, 0x02, 0x02, 0x02, 0x01, 0x01, 0x01, 0x01, 0x01,
+    0x02, 0x02, 0x02, 0x02, 0x02, 0x01, 0x01, 0x01, 0x01, 0x01};
+
+  uint8_t output_data[FX_ArraySize(expected_data)];
   memset(output_data, 0, sizeof(output_data));
   uint32_t output_size = FX_ArraySize(output_data);
 
-  EXPECT_EQ(CFX_GifDecodeStatus::Success,
-            decoder->Decode(image_data, image_size, output_data, &output_size));
-  uint8_t expected_data[] = {
-      0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x02, 0x02, 0x02, 0x02, 0x01, 0x01,
-      0x01, 0x01, 0x01, 0x02, 0x02, 0x02, 0x02, 0x02, 0x01, 0x01, 0x01, 0x01,
-      0x01, 0x02, 0x02, 0x02, 0x02, 0x02, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00,
-      0x00, 0x02, 0x02, 0x02, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x02,
-      0x02, 0x02, 0x02, 0x02, 0x02, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01, 0x01,
-      0x02, 0x02, 0x02, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01, 0x01, 0x02, 0x02,
-      0x02, 0x02, 0x02, 0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x02, 0x02, 0x02,
-      0x02, 0x01, 0x01, 0x01, 0x01, 0x01, 0x02, 0x02, 0x02, 0x02, 0x02, 0x01,
-      0x01, 0x01, 0x01, 0x01};
+  EXPECT_EQ(
+      CFX_GifDecodeStatus::Success,
+      decompressor->Decode(image_data, image_size, output_data, &output_size));
 
   EXPECT_EQ(FX_ArraySize(output_data), output_size);
   EXPECT_TRUE(0 == memcmp(expected_data, output_data, sizeof(expected_data)));
@@ -128,9 +198,8 @@ TEST(CFX_LZWDecompressor, HandleColourCodeOutOfPalette) {
   uint8_t palette_exp = 0x2;  // Image uses 10 colours, so the palette exp
                               // should be 3, 2^(3+1) = 16 colours.
   uint8_t code_exp = 0x4;
-
-  auto decoder = CFX_LZWDecompressor::Create(palette_exp, code_exp);
-  ASSERT_NE(nullptr, decoder);
+  auto decompressor = CFX_LZWDecompressor::Create(palette_exp, code_exp);
+  ASSERT_NE(nullptr, decompressor);
 
   uint8_t image_data[] = {0x30, 0xC9, 0x49, 0x81, 0xBD, 0x78, 0xE8, 0xCD,
                           0x89, 0xFF, 0x60, 0x20, 0x8E, 0xE4, 0x61, 0x9E,
@@ -138,10 +207,11 @@ TEST(CFX_LZWDecompressor, HandleColourCodeOutOfPalette) {
                           0xCF, 0x74, 0x61, 0xDF, 0x78, 0x04};
   uint32_t image_size = FX_ArraySize(image_data);
 
-  uint8_t output_data[100];
+  uint8_t output_data[100];  // The uncompressed data is for a 10x10 image
   memset(output_data, 0, sizeof(output_data));
   uint32_t output_size = FX_ArraySize(output_data);
 
-  EXPECT_EQ(CFX_GifDecodeStatus::Error,
-            decoder->Decode(image_data, image_size, output_data, &output_size));
+  EXPECT_EQ(
+      CFX_GifDecodeStatus::Error,
+      decompressor->Decode(image_data, image_size, output_data, &output_size));
 }