The diff-delta code can exhibit O(m*n) behavior with some patological
data set where most hash entries end up in the same hash bucket.
To prevent this, a limit is imposed to the number of entries that can
exist in the same hash bucket.
Because of the above the code is a tiny bit more expensive on average,
even if some small optimizations were added as well to atenuate the
overhead. But the problematic samples used to diagnoze the issue are now
orders of magnitude less expensive to process with only a slight loss in
compression.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
Testing for realloc and size limit can be done with only one test per
loop. Make it so and fix a theoretical off-by-one comparison error in
the process.
The output buffer memory allocation is also bounded by max_size when
specified.
Finally make some variable unsigned to allow the handling of files up to
4GB in size instead of 2GB.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
Since we already depend on zlib, we don't need to define our
own adler32(). Spotted by oprofile.
Signed-off-by: Peter Eriksen <s022018@student.dtu.dk>
Signed-off-by: Junio C Hamano <junkio@cox.net>
This patch removes unused remnants of the original xdiff source.
No functional change. Possible tiny speed improvement.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
Delta computation with an empty blob used to punt and returned NULL.
This commit allows creation with empty blob; all combination of
empty->empty, empty->something, and something->empty are allowed.
Signed-off-by: Junio C Hamano <junkio@cox.net>
This is a wrap-up patch including all the cleanups I've done to the
delta code and its usage. The most important change is the
factorization of the delta header handling code.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Since the delta data format is not tied to any actual git object
anymore, now is the time to add a small improvement to the delta data
header as it is been done for packed object header. This patch allows
for reducing the delta header of about 2 bytes and makes for simpler
code.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Anything that generates a delta to see if two objects are close usually
isn't interested in the delta ends up being bigger than some specified
size, and this allows us to stop delta generation early when that
happens.
This patch adds the basic library functions to create and replay delta
information. Also included is a test-delta utility to validate the
code.
diff-delta was based on LibXDiff written by Davide Libenzi
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Nicolas Pitre
Peter Eriksen
Junio C Hamano
Linus Torvalds