mirror of
https://github.com/emmanuel-marty/lzsa.git
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40 lines
1.3 KiB
Markdown
40 lines
1.3 KiB
Markdown
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# Stream format
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The stream format is composed of:
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* a header
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* one or more frames
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* a footer
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# Header format
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The 3-bytes LZSA header contains a signature and a traits byte:
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0 1 2
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0x7b 0x9e 7 6 5 4 3 2 1
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V V V Z Z Z Z
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<--- signature ---> <- traits ->
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Trait bits:
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* V: 3 bit code that indicates which block data encoding is used. 0 is LZSA1 and 2 is LZSA2.
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* Z: these bits in the traits are set to 0 for LZSA1 and LZSA2.
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# Frame format
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Each frame contains a 3-bytes length followed by block data that expands to up to 64 Kb of decompressed data. The block data is encoded either as LZSA1 or LZSA2 depending on the V bits of the traits byte in the header.
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0 1 2
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DSZ0 DSZ1 U|DSZ2
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* DSZ0 (length byte 0) contains bits 0-7 of the block data size
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* DSZ1 (length byte 1) contains bits 8-15 of the block data size
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* DSZ2 (bit 0 of length byte 2) contains bit 16 of the block data size
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* U (bit 7 of length byte 2) is set if the block data is uncompressed, and clear if the block data is compressed.
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* Bits 1..6 of length byte 2 are currently undefined and must be set to 0.
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# Footer format
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The stream ends with the EOD frame: the 3 length bytes are set to 0x00, 0x00, 0x00, and no block data follows.
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