Hawkynt

uABS (Binary Asymmetric Numeral Systems)

Binary variant of Asymmetric Numeral Systems. Each bit of the message is coded with the uABS transition pair against a 24-bit state that renormalizes one byte at a time. Probabilities come from an order-0 adaptive binary context tree, so no frequency table is transmitted. Distinct from the range variant (rANS) and from the table variants (FSE, tANS), which are implemented separately.

Properties

Property	Value
Category	Compression Algorithms
Sub-category	Entropy Coding
Security status	🎓 Educational Only
Complexity	Advanced
Inventor	Jarek Duda
Year	2009
Origin	Not specified
Source	algorithms/compression/ans.js

Security

Status: 🎓 Educational Only

No vulnerabilities are recorded for this implementation.

Documentation

• Asymmetric Numeral Systems (original paper)
• ANS with applications to data compression
• ANS on Wikipedia (uABS section)

References

• Jarek Duda homepage
• ryg_rans (range variant, for comparison)
• Finite State Entropy (table variant, for comparison)

Test vectors

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

Vector 1 — Empty input - length header only

Field	Value
input	(empty)
expected	00000000

Vector 2 — Single zero byte - eight bits coded at p=1/2

Field	Value
input	00
expected	010000000001000000

Vector 3 — Single byte 0x41 - renormalization emits one payload byte

Field	Value
input	41
expected	010000000001000041

Vector 4 — Single byte 0xFF - all-ones bit path

Field	Value
input	ff
expected	01000000000100017f

Vector 5 — Two identical bytes - pins the context adaptation rule

Field	Value
input	4141
expected	0200000000c82382a6

Vector 6 — Natural text round-trip

Source: Regression test for model desync

Field	Value
input	74686520717569636b2062726f776e20 666f78206a756d7073206f7665722074 6865206c617a7920646f672e20
expected	(empty)

Vector 7 — All 256 byte values round-trip

Source: Regression test for model desync

Field	Value
input	000102030405060708090a0b0c0d0e0f 101112131415161718191a1b1c1d1e1f 202122232425262728292a2b2c2d2e2f 303132333435363738393a3b3c3d3e3f 404142434445464748494a4b4c4d4e4f 505152535455565758595a5b5c5d5e5f 606162636465666768696a6b6c6d6e6f 707172737475767778797a7b7c7d7e7f 808182838485868788898a8b8c8d8e8f 909192939495969798999a9b9c9d9e9f a0a1a2a3a4a5a6a7a8a9aaabacadaeaf b0b1b2b3b4b5b6b7b8b9babbbcbdbebf c0c1c2c3c4c5c6c7c8c9cacbcccdcecf d0d1d2d3d4d5d6d7d8d9dadbdcdddedf e0e1e2e3e4e5e6e7e8e9eaebecedeeef f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff
expected	(empty)

Vector 8 — Long run round-trip

Source: Regression test for renormalization

Field	Value
input	5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a 5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a 5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a 5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a … (512 bytes; the full value is in the source)
expected	(empty)

Vector 9 — Alternating pattern round-trip

Source: Regression test for renormalization

Field	Value
input	aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55
expected	(empty)

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