[PATCH 3/4] Use binary searching on large buckets in git-describe.
- From
Shawn O. Pearce <spearce@spearce.org>
- Date
- Jan 13, 2007, 22:29 UTC
- Message-ID
- <20070113222900.GC18011@spearce.org>
- In-Reply-To
- <8e29bab8b4b9f53cbdc85e6e783bf3b5d3787f0f.1168727248.git.spearce@spearce.org>
If a project has a really huge number of tags (such as several thousand tags) then we are likely to have nearly a hundred tags in some buckets. Scanning those buckets as linked lists could take a large amount of time if done repeatedly during history traversal.
Since we are searching for a unique commit SHA1 we can sort all tags by commit SHA1 and perform a binary search within the bucket. Once we identify a particular tag as matching this commit we walk backwards within the bucket matches to make sure we pick up the highest priority tag for that commit, as the binary search may have landed us in the middle of a set of tags which point at the same commit.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org> --- builtin-describe.c | 29 +++++++++++++++++++++-------- 1 files changed, 21 insertions(+), 8 deletions(-)
diff --git a/builtin-describe.c b/builtin-describe.c index 582ef02..5d6865b 100644 --- a/builtin-describe.c +++ b/builtin-describe.c @@ -23,14 +23,24 @@ static struct commit_name { static struct commit_name *match(struct commit *cmit) { - unsigned char m = cmit->object.sha1[0]; - unsigned int i = names[m]; - struct commit_name **p = name_array[m]; - - while (i-- > 0) { - struct commit_name *n = *p++; - if (n->commit == cmit) - return n; + unsigned char level0 = cmit->object.sha1[0]; + struct commit_name **p = name_array[level0]; + unsigned int hi = names[level0]; + unsigned int lo = 0; + + while (lo < hi) { + unsigned int mi = (lo + hi) / 2; + int cmp = hashcmp(p[mi]->commit->object.sha1, + cmit->object.sha1); + if (!cmp) { + while (mi && p[mi - 1]->commit == cmit) + mi--; + return p[mi]; + } + if (cmp > 0) + hi = mi; + else + lo = mi+1; } return NULL; } @@ -95,7 +105,10 @@ static int compare_names(const void *_a, const void *_b) struct commit_name *b = *(struct commit_name **)_b; unsigned long a_date = a->commit->date; unsigned long b_date = b->commit->date; + int cmp = hashcmp(a->commit->object.sha1, b->commit->object.sha1); + if (cmp) + return cmp; if (a->prio != b->prio) return b->prio - a->prio; return (a_date > b_date) ? -1 : (a_date == b_date) ? 0 : 1;
-- 1.5.0.rc1.g4494