Hawkynt

LZFSE

Apple’s Lempel-Ziv Finite State Entropy compression algorithm. Splits the LZ77 parse into literal/length/distance streams and entropy-codes each with FSE (tANS), with an overflow stream for values outside the small direct symbol alphabet. Follows LZFSE’s documented shape but is not a byte-compatible reproduction of Apple’s real bitstream (whose bucket tables are unpublished).

Properties

Property	Value
Category	Compression Algorithms
Sub-category	Dictionary
Security status	🎓 Educational Only
Complexity	Advanced
Inventor	Apple Inc.
Year	2015
Origin	🇺🇸 United States
Source	algorithms/compression/lzfse.js

Security

Status: 🎓 Educational Only

No vulnerabilities are recorded for this implementation.

Documentation

• LZFSE GitHub Repository (Apple reference implementation)
• LZFSE Wikipedia
• Apple Developer Documentation

References

• LZFSE GitHub Repository
• Apple’s Compression Framework
• LZFSE Technical Analysis

Test vectors

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

Vector 1 — Empty input

Field	Value
input	(empty)
expected	00000000000000000000000006000000 05000020002000000000000000000000 0000000000000000000000000000

Vector 2 — Single byte literal

Field	Value
input	41
expected	01000000000000000100000008000000 05010000002000200000000000000000 00000000000000000000000088000000 05410000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 0000000000200020

Vector 3 — Text with no repetition - all literals

Field	Value
input	48656c6c6f20576f726c64
expected	0b000000000000000b0000001c000000 050b0000000000000000000000000000 00000000000000000020002000000000 00000000000000000000000000000000 … (306 bytes; the full value is in the source)

Vector 4 — Structured pattern with clear repetition

Field	Value
input	616263646566616263646566
expected	0c000000010000000600000012000000 05060010000000000000000000000010 0046000000000a000000050200000000 00200020000000001200000005060000 … (298 bytes; the full value is in the source)

Vector 5 — Repeated text sample (4x)

Field	Value
input	74686520717569636b2062726f776e20 666f78206a756d7073206f7665722074 6865206c617a7920646f672e20746865 20717569636b2062726f776e20666f78 206a756d7073206f7665722074686520 6c617a7920646f672e20746865207175 69636b2062726f776e20666f78206a75 6d7073206f76657220746865206c617a 7920646f672e2074686520717569636b 2062726f776e20666f78206a756d7073 206f76657220746865206c617a792064 6f672e20
expected	b4000000030000002800000045000000 051f0010000000000000000000000000 00000000000800000000000000000000 00000000000000000000000000000000 … (534 bytes; the full value is in the source)

Vector 6 — 256 repeated bytes

Field	Value
input	61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161 61616161616161616161616161616161
expected	00010000010000000100000008000000 05010010001000460000000044000000 051f0000000000000000000000000000 00000000000000000000000000000000 … (328 bytes; the full value is in the source)

Vector 7 — All 256 byte values

Field	Value
input	000102030405060708090a0b0c0d0e0f 101112131415161718191a1b1c1d1e1f 202122232425262728292a2b2c2d2e2f 303132333435363738393a3b3c3d3e3f 404142434445464748494a4b4c4d4e4f 505152535455565758595a5b5c5d5e5f 606162636465666768696a6b6c6d6e6f 707172737475767778797a7b7c7d7e7f 808182838485868788898a8b8c8d8e8f 909192939495969798999a9b9c9d9e9f a0a1a2a3a4a5a6a7a8a9aaabacadaeaf b0b1b2b3b4b5b6b7b8b9babbbcbdbebf c0c1c2c3c4c5c6c7c8c9cacbcccdcecf d0d1d2d3d4d5d6d7d8d9dadbdcdddedf e0e1e2e3e4e5e6e7e8e9eaebecedeeef f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff
expected	00010000000000000001000044000000 051f0000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 … (884 bytes; the full value is in the source)

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