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120 lines
4.3 KiB
C++
120 lines
4.3 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/* Various simple compression/decompression functions. */
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#ifndef mozilla_Compression_h_
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#define mozilla_Compression_h_
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#include "mozilla/Types.h"
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#include "mozilla/Assertions.h"
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namespace mozilla {
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namespace Compression {
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/**
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* LZ4 is a very fast byte-wise compression algorithm.
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*
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* Compared to Google's Snappy it is faster to compress and decompress and
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* generally produces output of about the same size.
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*
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* Compared to zlib it compresses at about 10x the speed, decompresses at about
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* 4x the speed and produces output of about 1.5x the size.
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*/
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class LZ4
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{
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public:
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/**
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* Compresses |aInputSize| bytes from |aSource| into |aDest|. Destination
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* buffer must be already allocated, and must be sized to handle worst cases
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* situations (input data not compressible). Worst case size evaluation is
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* provided by function maxCompressedSize()
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*
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* @param aInputSize is the input size. Max supported value is ~1.9GB
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* @return the number of bytes written in buffer |aDest|
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*/
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static MFBT_API size_t
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compress(const char* aSource, size_t aInputSize, char* aDest);
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/**
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* Compress |aInputSize| bytes from |aSource| into an output buffer
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* |aDest| of maximum size |aMaxOutputSize|. If it cannot achieve it,
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* compression will stop, and result of the function will be zero,
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* |aDest| will still be written to, but since the number of input
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* bytes consumed is not returned the result is not usable.
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*
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* This function never writes outside of provided output buffer.
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*
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* @param aInputSize is the input size. Max supported value is ~1.9GB
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* @param aMaxOutputSize is the size of the destination buffer (which must
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* be already allocated)
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* @return the number of bytes written in buffer |aDest| or 0 if the
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* compression fails
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*/
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static MFBT_API size_t
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compressLimitedOutput(const char* aSource, size_t aInputSize, char* aDest,
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size_t aMaxOutputSize);
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/**
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* If the source stream is malformed, the function will stop decoding
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* and return a negative result, indicating the byte position of the
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* faulty instruction
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*
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* This function never writes outside of provided buffers, and never
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* modifies input buffer.
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*
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* Note: destination buffer must be already allocated, and its size must be a
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* minimum of |aOutputSize| bytes.
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*
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* @param aOutputSize is the output size, therefore the original size
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* @return the number of bytes read in the source buffer
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*/
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static MFBT_API bool
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decompress(const char* aSource, char* aDest, size_t aOutputSize);
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/**
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* If the source stream is malformed, the function will stop decoding
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* and return false.
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*
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* This function never writes beyond aDest + aMaxOutputSize, and is
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* therefore protected against malicious data packets.
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*
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* Note: Destination buffer must be already allocated. This version is
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* slightly slower than the decompress without the aMaxOutputSize.
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*
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* @param aInputSize is the length of the input compressed data
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* @param aMaxOutputSize is the size of the destination buffer (which must be
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* already allocated)
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* @param aOutputSize the actual number of bytes decoded in the destination
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* buffer (necessarily <= aMaxOutputSize)
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*/
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static MFBT_API bool
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decompress(const char* aSource, size_t aInputSize, char* aDest,
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size_t aMaxOutputSize, size_t* aOutputSize);
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/*
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* Provides the maximum size that LZ4 may output in a "worst case"
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* scenario (input data not compressible) primarily useful for memory
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* allocation of output buffer.
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* note : this function is limited by "int" range (2^31-1)
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*
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* @param aInputSize is the input size. Max supported value is ~1.9GB
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* @return maximum output size in a "worst case" scenario
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*/
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static inline size_t maxCompressedSize(size_t aInputSize)
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{
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size_t max = (aInputSize + (aInputSize / 255) + 16);
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MOZ_ASSERT(max > aInputSize);
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return max;
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}
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};
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} /* namespace Compression */
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} /* namespace mozilla */
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#endif /* mozilla_Compression_h_ */
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