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112 lines
3.4 KiB
C++
112 lines
3.4 KiB
C++
/* 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 file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef SeekableZStream_h
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#define SeekableZStream_h
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#include "Zip.h"
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/**
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* Seekable compressed stream are created by splitting the original
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* decompressed data in small chunks and compress these chunks
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* individually.
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*
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* The seekable compressed file format consists in a header defined below,
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* followed by a table of 32-bits words containing the offsets for each
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* individual compressed chunk, then followed by the compressed chunks.
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*/
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#pragma pack(1)
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struct SeekableZStreamHeader: public Zip::SignedEntity<SeekableZStreamHeader>
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{
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SeekableZStreamHeader()
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: Zip::SignedEntity<SeekableZStreamHeader>(magic)
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, totalSize(0), chunkSize(0), nChunks(0), lastChunkSize(0), windowBits(0) { }
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/* Reuse Zip::SignedEntity to handle the magic number used in the Seekable
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* ZStream file format. The magic number is "SeZz". */
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static const uint32_t magic = 0x7a5a6553;
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/* Total size of the stream, including the 4 magic bytes. */
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le_uint32 totalSize;
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/* Chunk size */
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le_uint32 chunkSize;
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/* Number of chunks */
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le_uint32 nChunks;
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/* Size of last chunk (> 0, <= Chunk size) */
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le_uint16 lastChunkSize;
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/* windowBits value used when deflating */
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signed char windowBits;
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/* Padding */
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unsigned char unused;
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};
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#pragma pack()
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MOZ_STATIC_ASSERT(sizeof(SeekableZStreamHeader) == 5 * 4,
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"SeekableZStreamHeader should be 5 32-bits words");
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/**
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* Helper class used to decompress Seekable ZStreams.
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*/
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class SeekableZStream {
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public:
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/* Initialize from the given buffer. Returns whether initialization
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* succeeded (true) or failed (false). */
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bool Init(const void *buf, size_t length);
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/* Decompresses starting from the given chunk. The decompressed data is
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* stored at the given location. The given length, in bytes, indicates
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* how much data to decompress. If length is 0, then exactly one chunk
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* is decompressed.
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* Returns whether decompression succeeded (true) or failed (false). */
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bool Decompress(void *where, size_t chunk, size_t length = 0);
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/* Decompresses the given chunk at the given address. If a length is given,
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* only decompresses that amount of data instead of the entire chunk.
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* Returns whether decompression succeeded (true) or failed (false). */
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bool DecompressChunk(void *where, size_t chunk, size_t length = 0);
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/* Returns the uncompressed size of the complete zstream */
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const size_t GetUncompressedSize() const
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{
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return (offsetTable.numElements() - 1) * chunkSize + lastChunkSize;
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}
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/* Returns the chunk size of the given chunk */
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const size_t GetChunkSize(size_t chunk = 0) const {
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return (chunk == offsetTable.numElements() - 1) ? lastChunkSize : chunkSize;
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}
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/* Returns the number of chunks */
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const size_t GetChunksNum() const {
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return offsetTable.numElements();
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}
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private:
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/* RAW Seekable SZtream buffer */
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const unsigned char *buffer;
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/* Total size of the stream, including the 4 magic bytes. */
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uint32_t totalSize;
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/* Chunk size */
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uint32_t chunkSize;
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/* Size of last chunk (> 0, <= Chunk size) */
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uint32_t lastChunkSize;
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/* windowBits value used when deflating */
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int windowBits;
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/* Offsets table */
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Array<le_uint32> offsetTable;
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};
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#endif /* SeekableZStream_h */
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