Genuine Context Tree Weighting (Willems/Shtarkov/Tjalkens): a depth-16 binary context tree with a Krichevsky-Trofimov estimator per node, recursively weighted between each node’s own estimate and the product of its children, driving a binary arithmetic coder. Distinct from “Context Predictor (order-2/1/0)” in ctw.js, which despite its historic filename is an unrelated most-frequent-symbol predictor.
| Property | Value |
|---|---|
| Category | Compression Algorithms |
| Sub-category | Context Mixing |
| Security status | 🎓 Educational Only |
| Complexity | Advanced |
| Inventor | Frans Willems, Yuri Shtarkov, Tjalling Tjalkens |
| Year | 1995 |
| Origin | 🇳🇱 Netherlands |
| Source | algorithms/compression/ctw-willems.js |
Status: 🎓 Educational Only
No vulnerabilities are recorded for this implementation.
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 |
00000000 |
Vector 2 — Single byte literal
| Field | Value |
|---|---|
input |
41 |
expected |
010000006280 |
Vector 3 — Two bytes
| Field | Value |
|---|---|
input |
4142 |
expected |
0200000062cf00 |
Vector 4 — Text with no repetition
| Field | Value |
|---|---|
input |
48656c6c6f20576f726c64 |
expected |
0b00000066312f2a8b787dd38a2b3780 |
Vector 5 — Repeated text sample (4x)
| Field | Value |
|---|---|
input |
74686520717569636b2062726f776e20 666f78206a756d7073206f7665722074 6865206c617a7920646f672e20746865 20717569636b2062726f776e20666f78 206a756d7073206f7665722074686520 6c617a7920646f672e20746865207175 69636b2062726f776e20666f78206a75 6d7073206f76657220746865206c617a 7920646f672e2074686520717569636b 2062726f776e20666f78206a756d7073 206f76657220746865206c617a792064 6f672e20 |
expected |
b400000077578191c1ef6951402bbff4 0fe06e7fad93efe76eb8f98e1d9de8bb 6a368862d7cdf641fdba96d3defdd470 4484af640788b71c09c0defd04d4ebfe 1e479d281c4c77864b08fd5b07143359 2a699635b9714ef58ca147a1bdb6360a 763ad1d9a0d36fd82886b218 |
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 |
0001000070e865c932a56d |
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 |
00010000244b9e5f41569b1e4e74c0ae 47a08ce9844e4ff26153655c8e96877c 32b6d6f2e2308caf9d1470a06095d867 ab488e38112ff7ab7038045b6bce6523 … (261 bytes; the full value is in the source) |