When we cannot generate a delta, we return NULL but leave delta_size
untouched. This is generally OK, as callers rely on NULL to decide if
the output is usable or not. But it can confuse compilers; in
particular, gcc 9.2.1 with "-flto -O3" complains in fast-import's
store_object() that delta_len may be used uninitialized.
Let's change the diff-delta code to set the size explicitly to 0 for a
NULL return. That silences the compiler and makes it easier to reason
about the result.
Reported-by: Stephan Beyer <s-beyer@gmx.net>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The delta format used in the packfile cannot reference data at
offset larger than what can be expressed in 4-byte, but the
generator for the data failed to make sure the offset does not
overflow. This has been corrected.
* mk/diff-delta-avoid-large-offset:
diff-delta: do not allow delta offset truncation
Prevent generating delta offsets beyond 4G, as the xdelta used in
the pack format cannot represent such large offset.
Signed-off-by: Martin Koegler <martin.koegler@chello.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The current delta code produces incorrect pack objects for files > 4GB,
because the size is copied from size_t field to "unsigned int" variables
during the encoding process.
Signed-off-by: Martin Koegler <martin.koegler@chello.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The code sequence ' (1u << i) < hsize && i < 31 ' is a multi step
process, whose first step requires that 'i' is already less that 31,
otherwise the result (1u << i) is undefined (and 'undef_val < hsize'
can therefore be assumed to be 'false'), and so the later test i < 31
can always be optimized away as dead code ('i' is already less than 31,
or the short circuit 'and' applies).
So we need to get rid of that code. One way would be to exchange the
order of the conditions, so the expression 'i < 31 && (1u << i) < hsize'
would remove that optimized unstable code already.
However when checking the previous lines in that function, we can deduce
that 'hsize' must always be smaller than (1u<<31), since 506049c7df
(fix >4GiB source delta assertion failure), because 'entries' is
capped at an upper bound of 0xfffffffeU, so 'hsize' contains a maximum
value of 0x3fffffff, which is smaller than (1u<<31), so the value of
'i' will never be larger than 31 and we can remove that condition
entirely.
Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Acked-by: Philip Oakley <philipoakley@iee.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When people try insane things such as delta-compressing 4GiB files, they
get this assertion:
diff-delta.c:285: create_delta_index: Assertion `packed_entry - (struct index_entry *)mem == entries' failed.
This happens because:
1) the 'entries' variable is an unsigned int
2) it is assigned with entries = (bufsize - 1) / RABIN_WINDOW
(that itself is not a problem unless bufsize > 4G * RABIN_WINDOW)
3) the buffer is indexed from top to bottom starting at
"data = buffer + entries * RABIN_WINDOW" and the multiplication
here does indeed overflows, making the resulting top of the buffer
much lower than expected.
This makes the number of actually produced index entries smaller than
what was computed initially, hence the assertion.
Furthermore, the current delta encoding format cannot represent offsets
into a reference buffer with more than 32 bits anyway. So let's just
limit the number of entries to what the delta format can encode.
Reported-by: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Due to problems at cam.org, my nico@cam.org email address is no longer
valid. From now on, nico@fluxnic.net should be used instead.
Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
aka don't do pointer arithmetics on structs that have a FLEX_ARRAY member,
or you'll end up believing your array is 1 cell off its real address.
Signed-off-by: Pierre Habouzit <madcoder@debian.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The previous hash bucket culling resulted in a somewhat unpredictable
number of hash bucket entries in the order of magnitude of HASH_LIMIT.
Replace this with a Bresenham-like algorithm leaving us with exactly
HASH_LIMIT entries by uniform culling.
Signed-off-by: David Kastrup <dak@gnu.org>
Acked-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In normal use cases, the performance wins are not overly impressive:
we get something like 5-10% due to the slightly better locality of
memory accesses using the packed structure.
However, since the data structure for index entries saves 33% of
memory on 32-bit platforms and 40% on 64-bit platforms, the behavior
when memory gets limited should be nicer.
This is a rather well-contained change. One obvious improvement would
be sorting the elements in one bucket according to their hash, then
using binary probing to find the elements with the right hash value.
As it stands, the output should be strictly the same as previously
unless one uses the option for limiting the amount of used memory, in
which case the created packs might be better.
Signed-off-by: David Kastrup <dak@gnu.org>
Acked-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
A particularly bad case was HASH_LIMIT <= hash_count[i] < 2*HASH_LIMIT:
in that case, only a single hash survived. For larger cases,
2*HASH_LIMIT was the actual limiting value after pruning.
Signed-off-by: David Kastrup <dak@gnu.org>
Acked-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Delta indices, at least on 64-bit platforms, tend to be larger than
the actual uncompressed data. As such, keeping track of this storage
is important if you want to successfully limit the memory size of your
pack window.
Squirrel away the total allocation size inside the delta_index struct,
and add an accessor "sizeof_delta_index" to access it.
Signed-off-by: Brian Downing <bdowning@lavos.net>
Acked-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Commit 83572c1a91 changed many
realloc to xrealloc. This change was made in diff-delta.c too,
although the code can handle an out of memory failure.
This patch reverts this change in diff-delta.c.
Signed-off-by: Martin Koegler <mkoegler@auto.tuwien.ac.at>
Signed-off-by: Junio C Hamano <junkio@cox.net>
There is actually nothing left from the original LibXDiff code I used
over 2 years ago, and even the GIT implementation has diverged quite a
bit from LibXDiff's at this point. Let's update the copyright notice
to better reflect that fact.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
Martin Koegler noted that create_delta() performs a new hash lookup
after every block copy encoding which are currently limited to 64KB.
In case of larger identical blocks, the next hash lookup would normally
point to the next 64KB block in the reference buffer and multiple block
copy operations will be consecutively encoded.
It is however possible that the reference buffer be sparsely indexed if
hash buckets have been trimmed down in create_delta_index() when hashing
of the reference buffer isn't well balanced. In that case the hash
lookup following a block copy might fail to match anything and the fact
that the reference buffer still matches beyond the previous 64KB block
will be missed.
Let's rework the code so that buffer comparison isn't bounded to 64KB
anymore. The match size should be as large as possible up front and
only then should multiple block copy be encoded to cover it all.
Also, fewer hash lookups will be performed in the end.
According to Martin, this patch should reduce his 92MB pack down to 75MB
with the dataset he has.
Tests performed on the Linux kernel repo show a slightly smaller pack and
a slightly faster repack.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
This is a mechanical clean-up of the way *.c files include
system header files.
(1) sources under compat/, platform sha-1 implementations, and
xdelta code are exempt from the following rules;
(2) the first #include must be "git-compat-util.h" or one of
our own header file that includes it first (e.g. config.h,
builtin.h, pkt-line.h);
(3) system headers that are included in "git-compat-util.h"
need not be included in individual C source files.
(4) "git-compat-util.h" does not have to include subsystem
specific header files (e.g. expat.h).
Signed-off-by: Junio C Hamano <junkio@cox.net>
This reverts commit 16854571aa.
Git as recent as v1.1.6 do not understand version 3 delta.
v1.2.0 is Ok and I personally would say it is old enough, but
the improvement between version 2 and version 3 delta is not
bit enough to justify breaking older clients.
We should resurrect this later, but when we do so we shold
make it conditional.
Signed-off-by: Junio C Hamano <junkio@cox.net>
It's been quite a while now that GIT is able to read version 3 packs.
Let's create them at last.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
Change places that use realloc, without a proper error path, to instead use
xrealloc. Drop an erroneous error path in the daemon code that used errno
in the die message in favour of the simpler xrealloc.
Signed-off-by: Jonas Fonseca <fonseca@diku.dk>
Signed-off-by: Junio C Hamano <junkio@cox.net>
(1 << i) < hspace is compared in the `int` space rather that in the
unsigned one. the result will be wrong if hspace is between 0x40000000
and 0x80000000.
Signed-off-by: Pierre Habouzit <madcoder@debian.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
The only visible change is that git-blame doesn't understand
"--compability" anymore, but it does accept "--compatibility" instead,
which is already documented.
Signed-off-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
ANSI C99 doesn't allow void-pointer arithmetic. This patch fixes this in
various ways. Usually the strategy that required the least changes was used.
Signed-off-by: Florian Forster <octo@verplant.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
When initializing a `flexible array member' the macro `FLEX_ARRAY' should be
used. This was forgotten in `diff-delta.c'.
Signed-off-by: Florian Forster <octo@verplant.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
It cannot be assumed that the given buffer will never be moved when
shrinking the allocated memory size with realloc(). So let's ignore
that optimization for now.
This patch makes Electric Fence happy on Linux.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Acked-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
It is useless to preserve multiple hash entries for consecutive blocks
with the same hash. Keeping only the first one will allow for matching
the longest string of identical bytes while subsequent blocks will only
allow for shorter matches. The backward matching code will match the
end of it as necessary.
This improves both performances (no repeated string compare with long
successions of identical bytes, or even small group of bytes), as well
as compression (less likely to need random hash bucket entry culling),
especially with sparse files.
With well behaved data sets this patch doesn't change much.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
This is my assembly freak side looking at generated code again. And
since create_delta() is certainly pretty high on the radar every bits
count. In this case shorter code is generated if hash_mask is not
copied to a local variable.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
This brings another small repacking speedup for sensibly the same pack
size. On the Linux kernel repo, git-repack -a -f is 3.7% faster for a
0.4% larger pack.
Credits to Geert Bosch who brought the Rabin's polynomial idea to my
attention.
This also eliminate the issue of adler32() reading past the data buffer,
as noticed by Johannes Schindelin.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
This patch splits the diff-delta interface into index creation and delta
generation. A wrapper is provided to preserve the diff-delta() call.
This will allow for an optimization in pack-objects.c where the source
object could be fixed and a full window of objects tentatively tried
against
that same source object without recomputing the source index each time.
This patch only restructure things, plus a couple cleanups for good
measure. There is no performance change yet.
Signed-off-by: Nicolas Pitre <nico@cam.org>
This patch makes for 3.4% smaller pack with the git repository, and
a bit more than 3% smaller pack with the kernel repository.
And so with _no_ measurable CPU difference.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
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>
Jeff King