lzw_decompressor.cpp

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// Copyright 2017 The PDFium Authors
// 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
 
#include "core/fxcodec/gif/lzw_decompressor.h"
 
#include <string.h>
 
#include <algorithm>
#include <memory>
#include <utility>
 
#include "core/fxcrt/fx_safe_types.h"
#include "third_party/base/memory/ptr_util.h"
 
namespace fxcodec {
 
std::unique_ptr<LZWDecompressor> LZWDecompressor::Create(uint8_t color_exp,
                                                         uint8_t code_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;
 
  // Private ctor.
  return pdfium::WrapUnique(new LZWDecompressor(color_exp, code_exp));
}
 
LZWDecompressor::LZWDecompressor(uint8_t color_exp, uint8_t code_exp)
    : code_size_(code_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)) {
  ClearTable();
}
 
LZWDecompressor::~LZWDecompressor() = default;
 
void LZWDecompressor::SetSource(const uint8_t* src_buf, uint32_t src_size) {
  next_in_ = src_buf;
  avail_in_ = src_size;
}
 
LZWDecompressor::Status LZWDecompressor::Decode(uint8_t* dest_buf,
                                                uint32_t* dest_size) {
  if (!next_in_ || !dest_buf || !dest_size)
    return Status::kError;
 
  if (avail_in_ == 0)
    return Status::kUnfinished;
 
  if (*dest_size == 0)
    return Status::kInsufficientDestSize;
 
  uint32_t i = 0;
  if (decompressed_next_ != 0) {
    uint32_t extracted_size = ExtractData(dest_buf, *dest_size);
    if (decompressed_next_ != 0)
      return Status::kInsufficientDestSize;
 
    dest_buf += extracted_size;
    i += extracted_size;
  }
 
  while (i <= *dest_size && (avail_in_ > 0 || bits_left_ >= code_size_cur_)) {
    if (code_size_cur_ > GIF_MAX_LZW_EXP)
      return Status::kError;
 
    if (avail_in_ > 0) {
      if (bits_left_ > 31)
        return Status::kError;
 
      FX_SAFE_UINT32 safe_code = *next_in_++;
      safe_code <<= bits_left_;
      safe_code |= code_store_;
      if (!safe_code.IsValid())
        return Status::kError;
 
      code_store_ = safe_code.ValueOrDie();
      --avail_in_;
      bits_left_ += 8;
    }
 
    while (bits_left_ >= code_size_cur_) {
      uint16_t code =
          static_cast<uint16_t>(code_store_) & ((1 << code_size_cur_) - 1);
      code_store_ >>= code_size_cur_;
      bits_left_ -= code_size_cur_;
      if (code == code_clear_) {
        ClearTable();
        continue;
      }
      if (code == code_end_) {
        *dest_size = i;
        return Status::kSuccess;
      }
 
      if (code_old_ != static_cast<uint16_t>(-1)) {
        if (code_next_ < GIF_MAX_LZW_CODE) {
          if (code == code_next_) {
            AddCode(code_old_, code_first_);
            if (!DecodeString(code))
              return Status::kError;
          } else if (code > code_next_) {
            return Status::kError;
          } else {
            if (!DecodeString(code))
              return Status::kError;
 
            uint8_t append_char = decompressed_[decompressed_next_ - 1];
            AddCode(code_old_, append_char);
          }
        }
      } else {
        if (!DecodeString(code))
          return Status::kError;
      }
 
      code_old_ = code;
      uint32_t extracted_size = ExtractData(dest_buf, *dest_size - i);
      if (decompressed_next_ != 0)
        return Status::kInsufficientDestSize;
 
      dest_buf += extracted_size;
      i += extracted_size;
    }
  }
 
  if (avail_in_ != 0)
    return Status::kError;
 
  *dest_size = i;
  return Status::kUnfinished;
}
 
void LZWDecompressor::ClearTable() {
  code_size_cur_ = code_size_ + 1;
  code_next_ = code_end_ + 1;
  code_old_ = static_cast<uint16_t>(-1);
  memset(code_table_, 0, sizeof(code_table_));
  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 LZWDecompressor::AddCode(uint16_t prefix_code, uint8_t append_char) {
  if (code_next_ == GIF_MAX_LZW_CODE)
    return;
 
  code_table_[code_next_].prefix = prefix_code;
  code_table_[code_next_].suffix = append_char;
  if (++code_next_ < GIF_MAX_LZW_CODE) {
    if (code_next_ >> code_size_cur_)
      code_size_cur_++;
  }
}
 
bool LZWDecompressor::DecodeString(uint16_t code) {
  decompressed_.resize(code_next_ - code_clear_ + 1);
  decompressed_next_ = 0;
 
  while (code >= code_clear_ && code <= code_next_) {
    if (code == code_table_[code].prefix ||
        decompressed_next_ >= decompressed_.size())
      return false;
 
    decompressed_[decompressed_next_++] = code_table_[code].suffix;
    code = code_table_[code].prefix;
  }
 
  if (code >= code_color_end_)
    return false;
 
  decompressed_[decompressed_next_++] = static_cast<uint8_t>(code);
  code_first_ = static_cast<uint8_t>(code);
  return true;
}
 
uint32_t LZWDecompressor::ExtractData(uint8_t* dest_buf, uint32_t dest_size) {
  if (dest_size == 0)
    return 0;
 
  uint32_t copy_size = dest_size <= decompressed_next_
                           ? dest_size
                           : static_cast<uint32_t>(decompressed_next_);
  std::reverse_copy(decompressed_.data() + decompressed_next_ - copy_size,
                    decompressed_.data() + decompressed_next_, dest_buf);
  decompressed_next_ -= copy_size;
  return copy_size;
}
 
}  // namespace fxcodec