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