Please explain what means partially compatible with the vcdiff

[JuniorJPDJ]

Hey, Can you please tell me more about what's partial in the compatibility between hdiffpatch and vcdiff? It would be nice if you could also write it in readme for others ;D Readme states this: partially compatible with the open-vcdiff and xdelta3 patch file format VCDIFF(RFC 3284).

[sisong]

run $hdiffz or $hpatchz, can see some info about VCDIFF.

1. $hdiffz -VCD can created a standard VCDIFF format diffFile, but diffFile used single source window size == oldFile size;
   if this diffFile patch by open-vcdiff or xdelta3, will used larger memory (all oldFile's data will be loaded in memory).
2. $hpatchz unspport some xdelta's diffFile, it's created by $xdelta3 -S djw or $xdelta3 -S fgk

( ref #316 )

[jpruciak]

so hdiffz creates fully compatible VCDIFF, but hpatchz can only apply patches created by hdiffz?

[sisong]

I'm sorry I didn't make the situation clear.

• $hdiffz -VCD ... created diffFile, uncompressed, compatible with VCDIFF format.
  $hpatchz & $open-vcdiff & $xdelta3 all can apply this diffFile;
  $hpatchz requires O(1) memory when patching; but $open-vcdiff & $xdelta3 maybe requires O(oldFileSize+newFileSize) memory when patching. (because the diffFile used the sourceWindowSize == oldFileSize )
• $hdiffz -VCD-compressLevel[-dictSize] ... created diffFile, compressed by 7zXZ, compatible $xdelta3 -S lzma.
  $hpatchz & $xdelta3 can apply it;
  $hpatchz requires O(3*dictSize) memory when patching;
  but $xdelta3 maybe requires O(oldFileSize+newFileSize+3*dictSize) memory when patching.
• $hpatchz support all diffFile created by $open-vcdiff (includes various parameter combinations and private formats), requires O(sourceWindowSize+targetWindowSize) memory when patching;
• $hpatchz support the diffFile created by $xdelta3 -S, requires O(sourceWindowSize+targetWindowSize) memory when patching;
• $hpatchz support the diffFile created by $xdelta3 -S lzma, requires O(sourceWindowSize+targetWindowSize+3*dictSize) memory when patching;
• $hpatchz unsupport the diffFile created by $xdelta3 -S djw or $xdelta3 -S fgk. (hpatchz not included djw&fgk's decompressor)