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VCDIFF is a format and an algorithm for delta encoding, described in IETF's RFC 3284. The algorithm is based on Jon Bentley and Douglas McIlroy's paper "Data Compression Using Long Common Strings" [1] written in 1999.[ citation needed] VCDIFF is used as one of the delta encoding algorithms in "Delta encoding in HTTP" ( RFC 3229) and was employed in Google's Shared Dictionary Compression Over HTTP technology, formerly used in their Chrome browser.
Delta instructions
VCDIFF has 3 delta instructions. ADD, COPY, and RUN. ADD adds a new sequence, COPY copies from an old sequence, and RUN adds repeated data.
Implementations
Free software implementations include xdelta (version 3) and open-vcdiff.
- Google's Shared Dictionary Compression Over HTTP proposal uses this algorithm, and was included in the Google Chrome browser, up to version 58. [2]
- xdelta - A tool, which is an Open Source VCDIFF delta compression implementation
- google/open-vcdiff - Another Open Source VCDIFF delta compression implementation
- vczip as part of vcodex and ast-open packages (also part of UWIN)
- diffable - Java implementation, but some kind of original modification of VCDIFF
- jvcdiff - Full decoder/encoder Java implementation of VCDIFF
- vcdiff-java - another Java implementation of VCDIFF
- Miscellaneous Utility Library - C# implementation, decoding only
- CyanDelta - Updates CyanogenMod ROMs using Xdelta3 patches.
See also
References
- ^ Bentley, Jon; McIlroy, Douglas (1999). Data compression using long common strings. DCC '99: Proceedings of the Conference on Data Compression. IEEE Computer Society. CiteSeerX 10.1.1.11.8470. doi: 10.1109/DCC.1999.755678.
- ^ "Intent to Unship: SDCH". Retrieved 2017-08-08.
External links
- RFC 3284 - The VCDIFF Generic Differencing and Compression Data Format
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