Eric Biggers wrote: > On Sun, Aug 10, 2014 at 11:18:49AM +0200, Jean-Pierre André wrote: >> Hi, >> >> Did you compare with the Microsoft implementation ? >> >> I have only checked the biggest file in IE7 update for WinXP >> (WINDOWS/ie7updates/KB963027-IE7/ieframe.dll) with >> cluster size 4096 : >> >> Original size 6066688 >> Microsoft implementation 3883008 (64.0%) >> current implementation 3682304 (60.7%) >> proposed implementation 3710976 (61.2%) > I have not done any comparisons with the Microsoft implementation yet. Is > there > a more precise way to test it than actually copying a file to a NTFS volume > from > Windows?
For a better way you would have to identify which is the dll which compresses , and submit compression tasks with some control over the durations. > I'm not surprised that it apparently produces a worse compression ratio than > NTFS-3g. Although it's impossible to know for sure what their algorithm does, > my expectation is that they use hash chains --- similar to my proposal, > perhaps > with a slightly less exhaustive search --- but use "greedy" parsing rather > than > "lazy" parsing. I had analyzed the difference of results, and I was surprised to find that the full length of the matching string was not always used (such as found a matching string at some position with a matching length of 20, but only used a length of 12 and the next match not being better than the expected 8 bytes), and there does not appear to be a fixed maximum length (when all bytes are the same, the matching length is 4095 as would be expected). They probably bargained the duration against the compression rate. > If there's a desire for even greater performance improvement, then "greedy" > parsing is the way to go. But it will degrade the compression ratio, maybe > placing it closer to the Microsoft implementation. > > Eric > ------------------------------------------------------------------------------ _______________________________________________ ntfs-3g-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/ntfs-3g-devel
