how the recovery volumes works?

i have seen they in winrar and tested it. if you have n recovery volumes then you can recover *any* n missing volumes. at first sight it seems to be a magic

i have thought a little about that. i invented a way to recover only one volume. you can do this in this way:
- xor all volumes (i mean xor first bytes from all volumes, then xor second bytes from all volumes...) and you get recovery volume,
- you can recover any missing volume by xoring all volumes you have (including recovery volume)
- you can recover only one missing volume,

the algorithm that recover any missing n volumes is included in unrar sources in files recvol.cpp and rs.cpp.

can you explain this algorithm for me in easy way?

sorry for bad english.

hmm, difficult question ??

Probably similar to .par files - http://www.slyck.com/ng.php?page=6

thanks, very much appreciated. this was exactly what i want.

glad to help