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authorBrian Downing <bdowning@lavos.net>2008-02-05 21:10:44 (GMT)
committerJunio C Hamano <gitster@pobox.com>2008-02-07 06:35:28 (GMT)
commit43fe901b71f81cdff142048dfc27e492c445d225 (patch)
tree1e3e8ad7f8f760a950643f4970f2daee2364b1b7 /git-compat-util.h
parent7a2078b4b00fb1c5d7b0bf8155778f79377b8f2f (diff)
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compat: Add simplified merge sort implementation from glibc
qsort in Windows 2000 (and various other C libraries) is a Quicksort with the usual O(n^2) worst case. Unfortunately, sorting Git trees seems to get very close to that worst case quite often: $ /git/gitbad runstatus # On branch master qsort, nmemb = 30842 done, 237838087 comparisons. This patch adds a simplified version of the merge sort that is glibc's qsort(3). As a merge sort, this needs a temporary array equal in size to the array that is to be sorted, but has a worst-case performance of O(n log n). The complexity that was removed is: * Doing direct stores for word-size and -aligned data. * Falling back to quicksort if the allocation required to perform the merge sort would likely push the machine into swap. Even with these simplifications, this seems to outperform the Windows qsort(3) implementation, even in Windows XP (where it is "fixed" and doesn't trigger O(n^2) complexity on trees). [jes: moved into compat/qsort.c, as per Johannes Sixt's suggestion] [bcd: removed gcc-ism, thanks to Edgar Toernig. renamed make variable per Junio's comment.] Signed-off-by: Brian Downing <bdowning@lavos.net> Signed-off-by: Steffen Prohaska <prohaska@zib.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'git-compat-util.h')
-rw-r--r--git-compat-util.h6
1 files changed, 6 insertions, 0 deletions
diff --git a/git-compat-util.h b/git-compat-util.h
index 4df90cb..0514604 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -426,4 +426,10 @@ static inline int strtol_i(char const *s, int base, int *result)
return 0;
}
+#ifdef INTERNAL_QSORT
+void git_qsort(void *base, size_t nmemb, size_t size,
+ int(*compar)(const void *, const void *));
+#define qsort git_qsort
+#endif
+
#endif