2.5.3 Processing Rules

 Input streams are compressed in units of 4096 bytes. The process of creating a chunk is complete if at least 4096 bytes of data or the remainder of the input buffer is compressed. If the data remains in the input buffer, the processing of a new chunk is started.

Lempel-Ziv compression does not require that the entirety of the data to which a compressed word refers actually be in the uncompressed buffer when the word is processed. In other words, it is not required that (U – displacement + length < U). Therefore, when processing a compressed word, data MUST be copied from the start of the uncompressed target region to the end—that is, the byte at (U – displacement) MUST be copied first, then (U – displacement + 1), and so on, because the compressed word might refer to data that will be written during decompression.

Some of the bits in a flag byte might not be used. To process compressed buffers, the size of the compressed chunk that is stored in the chunk header MUST be used to determine the position of the last valid byte in the chunk. The size value MUST ignore flag bits that correspond to bytes outside the chunk.

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