Move LZW decoder out of fx_gif

CGifLZWDecoder has been moved out into its own file, name changed to
CFX_LZWDecoder, member variable names updated, creation pattern
changed, and unit tests added.

Wrt the creation pattern, there is no longer a constructor and 2
initialization methods that need to be called. Instead all of the
initialization is done as part of the constructor. A wrapper has been
added for generating a std::unique_ptr<CFX_LZWDecoder>, so that params
can be validated.

BUG=pdfium:900,pdfium:901,pdfium:903,pdfium:904

Change-Id: Idcbe773f7fb18b08e64d5a89bfd87d4801332c53
Reviewed-on: https://pdfium-review.googlesource.com/14814
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Ryan Harrison <rharrison@chromium.org>

1 files changed, 55 insertions, 0 deletions

diff --git a/core/fxcodec/lgif/cfx_lzwdecoder.h b/core/fxcodec/lgif/cfx_lzwdecoder.h
new file mode 100644
index 0000000000..913df670c6
--- /dev/null
+++ b/core/fxcodec/lgif/cfx_lzwdecoder.h
@@ -0,0 +1,55 @@
+// Copyright 2017 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
+
+#ifndef CORE_FXCODEC_LGIF_CFX_LZWDECODER_H_
+#define CORE_FXCODEC_LGIF_CFX_LZWDECODER_H_
+
+#include <memory>
+#include <vector>
+
+#include "core/fxcodec/lgif/fx_gif.h"
+
+class CFX_LZWDecoder {
+ public:
+  struct tag_Table {
+    uint16_t prefix;
+    uint8_t suffix;
+  };
+
+  // Returns nullptr on error
+  static std::unique_ptr<CFX_LZWDecoder> Create(uint8_t color_exp,
+                                                uint8_t code_exp);
+  ~CFX_LZWDecoder();
+
+  GifDecodeStatus Decode(uint8_t* src_buf,
+                         uint32_t src_size,
+                         uint8_t* des_buf,
+                         uint32_t* des_size);
+
+ private:
+  CFX_LZWDecoder(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);
+
+  uint8_t code_size_;
+  uint8_t code_size_cur_;
+  uint16_t code_color_end_;
+  uint16_t code_clear_;
+  uint16_t code_end_;
+  uint16_t code_next_;
+  uint8_t code_first_;
+  uint8_t stack_[GIF_MAX_LZW_CODE];
+  size_t stack_size_;
+  tag_Table code_table_[GIF_MAX_LZW_CODE];
+  uint16_t code_old_;
+  uint8_t* next_in_;
+  uint32_t avail_in_;
+  uint8_t bits_left_;
+  uint32_t code_store_;
+};
+
+#endif  // CORE_FXCODEC_LGIF_CFX_LZWDECODER_H_