gecko-dev/mfbt/Compression.h

117 lines
4.3 KiB
C++

/* -*- 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 inline 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_ */