DEFLATE Compressed Data Format Specification version 1.3 (RFC1951)

Network Working Group                                         P. Deutsch

Request for Comments: 1951                           Aladdin Enterprises

Category: Informational                                         May 1996

        DEFLATE Compressed Data Format Specification version 1.3

Status of This Memo

   This memo provides information for the Internet community.  This memo

   does not specify an Internet standard of any kind.  Distribution of

   this memo is unlimited.

IESG Note:

   The IESG takes no position on the validity of any Intellectual

   Property Rights statements contained in this document.

Notices

   Copyright (c) 1996 L. Peter Deutsch

   Permission is granted to copy and distribute this document for any

   purpose and without charge, including translations into other

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   copyright notice and this notice are preserved, and that any

   substantive changes or deletions from the original are clearly

   marked.

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   HTML format can be found at the URL

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Abstract

   This specification defines a lossless compressed data format that

   compresses data using a combination of the LZ77 algorithm and Huffman

   coding, with efficiency comparable to the best currently available

   general-purpose compression methods.  The data can be produced or

   consumed, even for an arbitrarily long sequentially presented input

   data stream, using only an a priori bounded amount of intermediate

   storage.  The format can be implemented readily in a manner not

   covered by patents.

Deutsch                      Informational                      [Page 1]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996

Table of Contents

   1. Introduction ................................................... 2

      1.1. Purpose ................................................... 2

      1.2. Intended audience ......................................... 3

      1.3. Scope ..................................................... 3

      1.4. Compliance ................................................ 3

      1.5.  Definitions of terms and conventions used ................ 3

      1.6. Changes from previous versions ............................ 4

   2. Compressed representation overview ............................. 4

   3. Detailed specification ......................................... 5

      3.1. Overall conventions ....................................... 5

          3.1.1. Packing into bytes .................................. 5

      3.2. Compressed block format ................................... 6

          3.2.1. Synopsis of prefix and Huffman coding ............... 6

          3.2.2. Use of Huffman coding in the "deflate" format ....... 7

          3.2.3. Details of block format ............................. 9

          3.2.4. Non-compressed blocks (BTYPE=00) ................... 11

          3.2.5. Compressed blocks (length and distance codes) ...... 11

          3.2.6. Compression with fixed Huffman codes (BTYPE=01) .... 12

          3.2.7. Compression with dynamic Huffman codes (BTYPE=10) .. 13

      3.3. Compliance ............................................... 14

   4. Compression algorithm details .........................