contents:2.∞ = Huffman encoded data stream until end of block (max. *.delta_bit_length:1.40 = 0=>next symbol 1=>alter length start_huffman_length:5 = 0.20 starting bit length for Huffman deltas *.selector_list:1.6 = zero-terminated bit runs (0.62) of MTF'ed Huffman table (*selectors_used) selectors_used:15 = number of times that the Huffman tables are swapped (each 50 symbols) huffman_groups:3 = 2.6 number of different Huffman tables in use huffman_used_bitmaps:0.256 = bitmap, of symbols used, present/not present (multiples of 16) huffman_used_map:16 = bitmap, of ranges of 16 bytes, present/not present origPtr:24 = starting pointer into BWT for after untransform In the worst case, it can cause an expansion of 1.25, and in the best case, a reduction to normal, 1=>randomised (deprecated) Runs of symbols are always transformed after 4 consecutive symbols, even if the run-length is set to zero, to keep the transformation reversible. Thus the sequence AAAAAAABBBBCCCD is replaced with AAAA\3BBBB\0CCCD, where \3 and \0 represent byte values 3 and 0 respectively. Sparse bit array showing which symbols are used.Īny sequence of 4 to 255 consecutive duplicate symbols is replaced by the first 4 symbols and a repeat length between 0 and 251.Delta encoding (Δ) of Huffman-code bit lengths.Unary base-1 encoding of Huffman table selection.Selection between multiple Huffman tables.Run-length encoding (RLE) of MTF result.Burrows–Wheeler transform (BWT), or block sorting.Run-length encoding (RLE) of initial data.JSTOR ( August 2021) ( Learn how and when to remove this template message)īzip2 uses several layers of compression techniques stacked on top of each other, which occur in the following order during compression and the reverse order during decompression:.Unsourced material may be challenged and removed.
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