mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-12-05 12:05:22 +00:00
2a0942be41
--HG-- extra : rebase_source : 668cd394806203ddfa34bd4f226335ff26c846b5
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 -*- */
|
|
/* 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/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 |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 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, and its size must be a
|
|
* minimum of |aOutputSize| bytes.
|
|
*
|
|
* @param aOutputSize 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* 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)
|
|
*/
|
|
static MFBT_API 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_ */
|