Microsoft’s LZ77+Huffman compression algorithm ([MS-XCA]), used in WIM images, NTFS, and Hyper-V. Splits data into 64KB chunks, each with its own 512-symbol canonical Huffman table (256 literals + 256 length/offset-class match symbols) over an LSB-first, 16-bit-word-packed bit stream.
| Property | Value |
|---|---|
| Category | Compression Algorithms |
| Sub-category | Dictionary-based |
| Security status | Not classified |
| Complexity | Advanced |
| Inventor | Microsoft |
| Year | 2014 |
| Origin | 🇺🇸 United States |
| Source | algorithms/compression/xpress.js |
Status: not classified — treat as unverified.
No vulnerabilities are recorded for this implementation.
3 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 — Highly repetitive input (64 ‘A’ bytes)
| Field | Value |
|---|---|
roundTripOnly |
Yes |
input |
41414141414141414141414141414141 41414141414141414141414141414141 41414141414141414141414141414141 41414141414141414141414141414141 |
expected |
(empty) |
Vector 3 — Text sample
| Field | Value |
|---|---|
roundTripOnly |
Yes |
input |
74686520717569636b2062726f776e20 666f78206a756d7073206f7665722074 6865206c617a7920646f672e20746865 20717569636b2062726f776e20666f78 2e |
expected |
(empty) |