Hawkynt

Shrink

PKZIP method 1 (Shrinking): dynamic LZW coding with encoder-controlled variable code width (9-13 bits) and partial dictionary clearing, which frees only leaf (unreferenced) entries instead of resetting the whole table.

Properties

Property	Value
Category	Compression Algorithms
Sub-category	Dictionary (LZW)
Security status	Not classified
Complexity	Advanced
Inventor	PKWARE, Inc. (based on Terry Welch’s LZW)
Year	1989
Origin	🇺🇸 United States
Source	algorithms/compression/shrink.js

Security

Status: not classified — treat as unverified.

No vulnerabilities are recorded for this implementation.

Documentation

• .ZIP File Format Specification (APPNOTE.TXT)
• ZIP (file format) - Wikipedia (Shrinking method)
• A Technique for High-Performance Data Compression (Welch, 1984)

References

• Info-ZIP unshrink.c (historical decoder notes)
• Lempel-Ziv-Welch - Wikipedia

Test vectors

5 vectors ship with this algorithm and run in the test suite. Byte values are hexadecimal.

Vector 1 — Empty input

Field	Value
input	(empty)
expected	00000000

Vector 2 — Single byte

Field	Value
input	41
expected	010000004100

Vector 3 — 256 repeated bytes

Field	Value
input	61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161
expected	0001000061020a1c48b0a0c18308132a5cc8b0a1c38710234a9c48b1a240

Vector 4 — Text sample repeated 4x

Field	Value
input	74686520717569636b2062726f776e20 666f78206a756d7073206f7665722074 6865206c617a7920646f672e20746865 20717569636b2062726f776e20666f78 206a756d7073206f7665722074686520 6c617a7920646f672e20746865207175 69636b2062726f776e20666f78206a75 6d7073206f76657220746865206c617a 7920646f672e2074686520717569636b 2062726f776e20666f78206a756d7073 206f76657220746865206c617a792064 6f672e20
expected	b400000074d0940111a74e9a316b4088 91f3e68e1b1066dee001a1a64e1b3873 40bcb153460e888003d984d193070499 37675c7c1448d02042850c1d429448d1 22468d1c3d82042192a449942a77163c 987061c387112756bc987163c7952147 963c99126a4ba2308fce546ab3694eab 3da7020501

Vector 5 — All 256 byte values

Field	Value
input	000102030405060708090a0b0c0d0e0f 101112131415161718191a1b1c1d1e1f 202122232425262728292a2b2c2d2e2f 303132333435363738393a3b3c3d3e3f 404142434445464748494a4b4c4d4e4f 505152535455565758595a5b5c5d5e5f 606162636465666768696a6b6c6d6e6f 707172737475767778797a7b7c7d7e7f 808182838485868788898a8b8c8d8e8f 909192939495969798999a9b9c9d9e9f a0a1a2a3a4a5a6a7a8a9aaabacadaeaf b0b1b2b3b4b5b6b7b8b9babbbcbdbebf c0c1c2c3c4c5c6c7c8c9cacbcccdcecf d0d1d2d3d4d5d6d7d8d9dadbdcdddedf e0e1e2e3e4e5e6e7e8e9eaebecedeeef f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff
expected	000100000002081840a0808103081228 58c0a08183071022489840a182850b18 3268d8c0a183870f2042881841a28489 132852a858c1a2858b173062c89841a3 … (292 bytes; the full value is in the source)

---

← All algorithms

This site is open source. Improve this page.