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rANS (Range Asymmetric Numeral Systems)

Advanced entropy coding using range-based asymmetric numeral systems for optimal compression efficiency. Provides arithmetic coding quality with faster processing through range-based state management and renormalization.

Properties

Property	Value
Category	Compression Algorithms
Sub-category	Entropy Coding
Security status	🎓 Educational Only
Complexity	Advanced
Inventor	Jarek Duda, Fabian Giesen
Year	2011
Origin	🌐 International
Source	algorithms/compression/rans.js

Security

Status: 🎓 Educational Only

No vulnerabilities are recorded for this implementation.

Documentation

• rANS Implementation
• ANS Entropy Coding
• Fabian Giesen Blog

References

• Asymmetric Numeral Systems
• Range Coding Theory
• rANS vs tANS Comparison
• Practical ANS Implementation

Test vectors

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

Vector 1 — Empty input - boundary case

Field	Value
input	(empty)
expected	(empty)

Vector 2 — Single character round-trip test

Field	Value
input	41
expected	(empty)

Vector 3 — Repeated characters round-trip test

Field	Value
input	41414141
expected	(empty)

Vector 4 — Alternating characters round-trip test

Field	Value
input	41424142
expected	(empty)

Vector 5 — Three symbols round-trip test

Field	Value
input	414243
expected	(empty)

Vector 6 — Skewed distribution round-trip test

Field	Value
input	414142
expected	(empty)

Vector 7 — Longer alternating input round-trip test (exercises renormalization)

Field	Value
input	4142414241424142
expected	(empty)

Vector 8 — All 256 byte values round-trip test

Source: Regression test for decoder/model desync

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

Vector 9 — Repeated phrase round-trip test

Source: Regression test for decoder/model desync

Field	Value
input	74686520717569636b2062726f776e20 666f78206a756d7073206f7665722074 6865206c617a7920646f672e20746865 20717569636b2062726f776e20666f78 206a756d7073206f7665722074686520 6c617a7920646f672e20746865207175 69636b2062726f776e20666f78206a75 6d7073206f76657220746865206c617a 7920646f672e2074686520717569636b 2062726f776e20666f78206a756d7073 206f76657220746865206c617a792064 6f672e20
expected	(empty)

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