The VCDIFF Generic Differencing and Compression Data Format

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RFC 3284                         VCDIFF                        June 2002


   Below are the details of the various items:

      Win_Indicator:
          This byte is a set of bits, as shown:

          7 6 5 4 3 2 1 0
         +-+-+-+-+-+-+-+-+
         | | | | | | | | |
         +-+-+-+-+-+-+-+-+
                      ^ ^
                      | |
                      | +-- VCD_SOURCE
                      +---- VCD_TARGET

         If bit 0 (VCD_SOURCE) is non-zero, this indicates that a
         segment of data from the "source" file was used as the
         corresponding source window of data to encode the target
         window.  The decoder will use this same source data segment to
         decode the target window.

         If bit 1 (VCD_TARGET) is non-zero, this indicates that a
         segment of data from the "target" file was used as the
         corresponding source window of data to encode the target
         window.  As above, this same source data segment is used to
         decode the target window.

         The Win_Indicator byte MUST NOT have more than one of the bits
         set (non-zero).  It MAY have none of these bits set.

         If one of these bits is set, the byte is followed by two
         integers to indicate respectively, the length and position of
         the source data segment in the relevant file.  If the indicator
         byte is zero, the target window was compressed by itself
         without comparing against another data segment, and these two
         integers are not included.

      The delta encoding of the target window:

         This contains the delta encoding of the target window, either
         in terms of the source data segment (i.e., VCD_SOURCE or
         VCD_TARGET was set) or by itself if no source window is
         specified.  This data format is discussed next.









Korn, et. al.               Standards Track                     [Page 9]