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2.3.1 Block Header

An LZXD block represents a sequence of compressed data that is encoded with the same set of Huffman trees, or a sequence of uncompressed data. There can be one or more LZXD blocks in a compressed stream (2), each with its own set of Huffman trees. Blocks do not have to start or end on a chunk boundary; blocks can span multiple chunks, or a single chunk can contain multiple blocks. The number of chunks is related to the size of the data being compressed, while the number of blocks is related to how well the data is compressed. The Block Type field, as specified in section 2.3.1.1, indicates which type of block follows, and the Block Size field, as specified in section 2.3.1.2, indicates the number of uncompressed bytes represented by the block. Following the generic block header is a type-specific header that describes the remainder of the block.

Field

Comments

Size

Block Type

See valid values in section 2.3.1.1

3 bits

Block Size most significant bit

Block size is the high 8 bits of 24

8 bits

Block Size byte 2

Block size is the middle 8 bits of 24

8 bits

Block Size least significant bit

Block size is the low 8 bits of 24

8 bits

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