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comparison: mfbt/Compression.h
mfbt/Compression.h
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| 1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ | |
| 2 /* This Source Code Form is subject to the terms of the Mozilla Public | |
| 3 * License, v. 2.0. If a copy of the MPL was not distributed with this | |
| 4 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ | |
| 5 | |
| 6 /* Various simple compression/decompression functions. */ | |
| 7 | |
| 8 #ifndef mozilla_Compression_h_ | |
| 9 #define mozilla_Compression_h_ | |
| 10 | |
| 11 #include "mozilla/Types.h" | |
| 12 #include "mozilla/Assertions.h" | |
| 13 | |
| 14 namespace mozilla { | |
| 15 namespace Compression { | |
| 16 | |
| 17 /** | |
| 18 * LZ4 is a very fast byte-wise compression algorithm. | |
| 19 * | |
| 20 * Compared to Google's Snappy it is faster to compress and decompress and | |
| 21 * generally produces output of about the same size. | |
| 22 * | |
| 23 * Compared to zlib it compresses at about 10x the speed, decompresses at about | |
| 24 * 4x the speed and produces output of about 1.5x the size. | |
| 25 * | |
| 26 */ | |
| 27 | |
| 28 class LZ4 | |
| 29 { | |
| 30 | |
| 31 public: | |
| 32 | |
| 33 /** | |
| 34 * Compresses 'inputSize' bytes from 'source' into 'dest'. | |
| 35 * Destination buffer must be already allocated, | |
| 36 * and must be sized to handle worst cases situations (input data not compressible) | |
| 37 * Worst case size evaluation is provided by function maxCompressedSize() | |
| 38 * | |
| 39 * @param inputSize is the input size. Max supported value is ~1.9GB | |
| 40 * @param return the number of bytes written in buffer dest | |
| 41 */ | |
| 42 static MFBT_API size_t compress(const char* source, size_t inputSize, char* dest); | |
| 43 | |
| 44 /** | |
| 45 * Compress 'inputSize' bytes from 'source' into an output buffer | |
| 46 * 'dest' of maximum size 'maxOutputSize'. If it cannot achieve it, | |
| 47 * compression will stop, and result of the function will be zero, | |
| 48 * 'dest' will still be written to, but since the number of input | |
| 49 * bytes consumed is not returned the result is not usable. | |
| 50 * | |
| 51 * This function never writes outside of provided output buffer. | |
| 52 * | |
| 53 * @param inputSize is the input size. Max supported value is ~1.9GB | |
| 54 * @param maxOutputSize is the size of the destination buffer (which must be already allocated) | |
| 55 * @return the number of bytes written in buffer 'dest' | |
| 56 or 0 if the compression fails | |
| 57 */ | |
| 58 static MFBT_API size_t compressLimitedOutput(const char* source, size_t inputSize, char* dest, | |
| 59 size_t maxOutputSize); | |
| 60 | |
| 61 /** | |
| 62 * If the source stream is malformed, the function will stop decoding | |
| 63 * and return a negative result, indicating the byte position of the | |
| 64 * faulty instruction | |
| 65 * | |
| 66 * This function never writes outside of provided buffers, and never | |
| 67 * modifies input buffer. | |
| 68 * | |
| 69 * note : destination buffer must be already allocated. | |
| 70 * its size must be a minimum of 'outputSize' bytes. | |
| 71 * @param outputSize is the output size, therefore the original size | |
| 72 * @return the number of bytes read in the source buffer | |
| 73 */ | |
| 74 static MFBT_API bool decompress(const char* source, char* dest, size_t outputSize); | |
| 75 | |
| 76 /** | |
| 77 * If the source stream is malformed, the function will stop decoding | |
| 78 * and return false. | |
| 79 * | |
| 80 * This function never writes beyond dest + maxOutputSize, and is | |
| 81 * therefore protected against malicious data packets. | |
| 82 * | |
| 83 * note : Destination buffer must be already allocated. | |
| 84 * This version is slightly slower than the decompress | |
| 85 * without the maxOutputSize | |
| 86 * | |
| 87 * @param inputSize is the length of the input compressed data | |
| 88 * @param maxOutputSize is the size of the destination buffer (which must be already allocated) | |
| 89 * @param outputSize the actual number of bytes decoded in the destination buffer (necessarily <= maxOutputSize) | |
| 90 | |
| 91 */ | |
| 92 static MFBT_API bool decompress(const char* source, size_t inputSize, char* dest, | |
| 93 size_t maxOutputSize, size_t *outputSize); | |
| 94 | |
| 95 /* | |
| 96 Provides the maximum size that LZ4 may output in a "worst case" | |
| 97 scenario (input data not compressible) primarily useful for memory | |
| 98 allocation of output buffer. | |
| 99 note : this function is limited by "int" range (2^31-1) | |
| 100 | |
| 101 @param inputSize is the input size. Max supported value is ~1.9GB | |
| 102 @return maximum output size in a "worst case" scenario | |
| 103 */ | |
| 104 static inline size_t maxCompressedSize(size_t inputSize) | |
| 105 { | |
| 106 size_t max = ((inputSize) + ((inputSize)/255) + 16); | |
| 107 MOZ_ASSERT(max > inputSize); | |
| 108 return max; | |
| 109 } | |
| 110 | |
| 111 }; | |
| 112 | |
| 113 } /* namespace Compression */ | |
| 114 } /* namespace mozilla */ | |
| 115 | |
| 116 #endif /* mozilla_Compression_h_ */ |
