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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[edit]

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.


Free software implementations include xdelta (version 3) and open-vcdiff.

See also[edit]


  1. ^ Bentley, Jon; McIlroy, Douglas (1999). Data compression using long common strings. DCC '99: Proceedings of the Conference on Data Compression. IEEE Computer Society. CiteSeerX doi:10.1109/DCC.1999.755678.
  2. ^ "Intent to Unship: SDCH". Retrieved 2017-08-08.

External links[edit]

  • RFC 3284 - The VCDIFF Generic Differencing and Compression Data Format