gecko/mfbt/Compression.h

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* Various simple compression/decompression functions. */

#ifndef mozilla_Compression_h_
#define mozilla_Compression_h_

#include "mozilla/Types.h"
#include "mozilla/Assertions.h"

namespace mozilla {
namespace Compression {

/**
 * LZ4 is a very fast byte-wise compression algorithm.
 *
 * Compared to Google's Snappy it is faster to compress and decompress and
 * generally produces output of about the same size.
 *
 * Compared to zlib it compresses at about 10x the speed, decompresses at about
 * 4x the speed and produces output of about 1.5x the size.
 *
 */

class LZ4
{

public:

  /**
   * Compresses 'inputSize' bytes from 'source' into 'dest'.
   * Destination buffer must be already allocated,
   * and must be sized to handle worst cases situations (input data not compressible)
   * Worst case size evaluation is provided by function LZ4_compressBound()
   *
   * @param inputSize is the input size. Max supported value is ~1.9GB
   * @param return the number of bytes written in buffer dest
   */
  static MFBT_API size_t compress(const char* source, size_t inputSize, char* dest);

  /**
   * Compress 'inputSize' bytes from 'source' into an output buffer
   * 'dest' of maximum size 'maxOutputSize'.  If it cannot achieve it,
   * compression will stop, and result of the function will be zero,
   * 'dest' will still be written to, but since the number of input
   * bytes consumed is not returned the result is not usable.
   *
   * This function never writes outside of provided output buffer.
   *
   * @param inputSize is the input size. Max supported value is ~1.9GB
   * @param maxOutputSize is the size of the destination buffer (which must be already allocated)
   * @return the number of bytes written in buffer 'dest'
             or 0 if the compression fails
  */
  static MFBT_API size_t compressLimitedOutput(const char* source, size_t inputSize, char* dest,
                                               size_t maxOutputSize);

  /**
   * If the source stream is malformed, the function will stop decoding
   * and return a negative result, indicating the byte position of the
   * faulty instruction
   *
   * This function never writes outside of provided buffers, and never
   * modifies input buffer.
   *
   * note : destination buffer must be already allocated.
   *        its size must be a minimum of 'outputSize' bytes.
   * @param outputSize is the output size, therefore the original size
   * @return the number of bytes read in the source buffer
  */
  static MFBT_API bool decompress(const char* source, char* dest, size_t outputSize);

  /**
   * If the source stream is malformed, the function will stop decoding
   * and return false.
   *
   * This function never writes beyond dest + maxOutputSize, and is
   * therefore protected against malicious data packets.
   *
   * note   : Destination buffer must be already allocated.
   *          This version is slightly slower than the decompress
   *          without the maxOutputSize
   *
   * @param inputSize is the length of the input compressed data
   * @param maxOutputSize is the size of the destination buffer (which must be already allocated)
   * @param outputSize the actual number of bytes decoded in the destination buffer (necessarily <= maxOutputSize)

  */
  static MFBT_API bool decompress(const char* source, size_t inputSize, char* dest,
                                  size_t maxOutputSize, size_t *outputSize);

  /*
    Provides the maximum size that LZ4 may output in a "worst case"
    scenario (input data not compressible) primarily useful for memory
    allocation of output buffer.
    note : this function is limited by "int" range (2^31-1)

    @param inputSize is the input size. Max supported value is ~1.9GB
    @return maximum output size in a "worst case" scenario
  */
  static MFBT_API size_t maxCompressedSize(size_t inputSize)
  {
      size_t max = ((inputSize) + ((inputSize)/255) + 16);
      MOZ_ASSERT(max > inputSize);
      return max;
  }

};

} /* namespace Compression */
} /* namespace mozilla */

#endif /* mozilla_Compression_h_ */