path: root/sha1-lookup.h
AgeCommit message (Collapse)Author
2019-05-05*.[ch]: manually align parameter listsDenton Liu
In previous patches, extern was mechanically removed from function declarations without care to formatting, causing parameter lists to be misaligned. Manually format changed sections such that the parameter lists should be realigned. Viewing this patch with 'git diff -w' should produce no output. Signed-off-by: Denton Liu <> Signed-off-by: Junio C Hamano <>
2019-05-05*.[ch]: remove extern from function declarations using spatchDenton Liu
There has been a push to remove extern from function declarations. Remove some instances of "extern" for function declarations which are caught by Coccinelle. Note that Coccinelle has some difficulty with processing functions with `__attribute__` or varargs so some `extern` declarations are left behind to be dealt with in a future patch. This was the Coccinelle patch used: @@ type T; identifier f; @@ - extern T f(...); and it was run with: $ git ls-files \*.{c,h} | grep -v ^compat/ | xargs spatch --sp-file contrib/coccinelle/noextern.cocci --in-place Files under `compat/` are intentionally excluded as some are directly copied from external sources and we should avoid churning them as much as possible. Signed-off-by: Denton Liu <> Signed-off-by: Junio C Hamano <>
2018-02-15packfile: refactor hash search with fanout tableJonathan Tan
Subsequent patches will introduce file formats that make use of a fanout array and a sorted table containing hashes, just like packfiles. Refactor the hash search in packfile.c into its own function, so that those patches can make use of it as well. Signed-off-by: Jonathan Tan <> Signed-off-by: Junio C Hamano <>
2017-08-25sha1-lookup: remove sha1_entry_pos() from header fileChristian Couder
Since f1068efefe (sha1_file: drop experimental GIT_USE_LOOKUP search, 2017-08-09) the definition of sha1_entry_pos() has been removed from "sha1-lookup.c", so there is no need anymore for its declaration in "sha1-lookup.h". Signed-off-by: Christian Couder <> Acked-by: Jeff King <> Signed-off-by: Junio C Hamano <>
2009-04-05sha1-lookup: add new "sha1_pos" function to efficiently lookup sha1Christian Couder
This function has been copied from the "patch_pos" function in "patch-ids.c" but an additional parameter has been added. The new parameter is a function pointer, that is used to access the sha1 of an element in the table. Signed-off-by: Christian Couder <> Signed-off-by: Junio C Hamano <>
2008-04-09sha1-lookup: more memory efficient search in sorted list of SHA-1Junio C Hamano
Currently, when looking for a packed object from the pack idx, a simple binary search is used. A conventional binary search loop looks like this: unsigned lo, hi; do { unsigned mi = (lo + hi) / 2; int cmp = "entry pointed at by mi" minus "target"; if (!cmp) return mi; "mi is the wanted one" if (cmp > 0) hi = mi; "mi is larger than target" else lo = mi+1; "mi is smaller than target" } while (lo < hi); "did not find what we wanted" The invariants are: - When entering the loop, 'lo' points at a slot that is never above the target (it could be at the target), 'hi' points at a slot that is guaranteed to be above the target (it can never be at the target). - We find a point 'mi' between 'lo' and 'hi' ('mi' could be the same as 'lo', but never can be as high as 'hi'), and check if 'mi' hits the target. There are three cases: - if it is a hit, we have found what we are looking for; - if it is strictly higher than the target, we set it to 'hi', and repeat the search. - if it is strictly lower than the target, we update 'lo' to one slot after it, because we allow 'lo' to be at the target and 'mi' is known to be below the target. If the loop exits, there is no matching entry. When choosing 'mi', we do not have to take the "middle" but anywhere in between 'lo' and 'hi', as long as lo <= mi < hi is satisfied. When we somehow know that the distance between the target and 'lo' is much shorter than the target and 'hi', we could pick 'mi' that is much closer to 'lo' than (hi+lo)/2, which a conventional binary search would pick. This patch takes advantage of the fact that the SHA-1 is a good hash function, and as long as there are enough entries in the table, we can expect uniform distribution. An entry that begins with for example "deadbeef..." is much likely to appear much later than in the midway of a reasonably populated table. In fact, it can be expected to be near 87% (222/256) from the top of the table. This is a work-in-progress and has switches to allow easier experiments and debugging. Exporting GIT_USE_LOOKUP environment variable enables this code. On my admittedly memory starved machine, with a partial KDE repository (3.0G pack with 95M idx): $ GIT_USE_LOOKUP=t git log -800 --stat HEAD >/dev/null 3.93user 0.16system 0:04.09elapsed 100%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (0major+55588minor)pagefaults 0swaps Without the patch, the numbers are: $ git log -800 --stat HEAD >/dev/null 4.00user 0.15system 0:04.17elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (0major+60258minor)pagefaults 0swaps In the same repository: $ GIT_USE_LOOKUP=t git log -2000 HEAD >/dev/null 0.12user 0.00system 0:00.12elapsed 97%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (0major+4241minor)pagefaults 0swaps Without the patch, the numbers are: $ git log -2000 HEAD >/dev/null 0.05user 0.01system 0:00.07elapsed 100%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (0major+8506minor)pagefaults 0swaps There isn't much time difference, but the number of minor faults seems to show that we are touching much smaller number of pages, which is expected. Signed-off-by: Junio C Hamano <>