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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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/Assertions.h"
#include "mozilla/Types.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 |aInputSize| bytes from |aSource| into |aDest|. 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 maxCompressedSize()
*
* @param aInputSize is the input size. Max supported value is ~1.9GB
* @return the number of bytes written in buffer |aDest|
*/
static MFBT_API size_t
compress(const char* aSource, size_t aInputSize, char* aDest);
/**
* Compress |aInputSize| bytes from |aSource| into an output buffer
* |aDest| of maximum size |aMaxOutputSize|. If it cannot achieve it,
* compression will stop, and result of the function will be zero,
* |aDest| 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 aInputSize is the input size. Max supported value is ~1.9GB
* @param aMaxOutputSize is the size of the destination buffer (which must
* be already allocated)
* @return the number of bytes written in buffer |aDest| or 0 if the
* compression fails
*/
static MFBT_API size_t
compressLimitedOutput(const char* aSource, size_t aInputSize, char* aDest,
size_t aMaxOutputSize);
/**
* If the source stream is malformed, the function will stop decoding
* and return false.
*
* This function never writes outside of provided buffers, and never
* modifies input buffer.
*
* Note: destination buffer must be already allocated, and its size must be a
* minimum of |aOutputSize| bytes.
*
* @param aOutputSize is the output size, therefore the original size
* @return true on success, false on failure
*/
static MFBT_API MOZ_MUST_USE bool
decompress(const char* aSource, char* aDest, size_t aOutputSize);
/**
* If the source stream is malformed, the function will stop decoding
* and return false.
*
* This function never writes beyond aDest + aMaxOutputSize, 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 aMaxOutputSize.
*
* @param aInputSize is the length of the input compressed data
* @param aMaxOutputSize is the size of the destination buffer (which must be
* already allocated)
* @param aOutputSize the actual number of bytes decoded in the destination
* buffer (necessarily <= aMaxOutputSize)
* @return true on success, false on failure
*/
static MFBT_API MOZ_MUST_USE bool
decompress(const char* aSource, size_t aInputSize, char* aDest,
size_t aMaxOutputSize, size_t* aOutputSize);
/*
* 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 aInputSize is the input size. Max supported value is ~1.9GB
* @return maximum output size in a "worst case" scenario
*/
static inline size_t maxCompressedSize(size_t aInputSize)
{
size_t max = (aInputSize + (aInputSize / 255) + 16);
MOZ_ASSERT(max > aInputSize);
return max;
}
};
} /* namespace Compression */
} /* namespace mozilla */
#endif /* mozilla_Compression_h_ */
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