mirror of
https://github.com/git/git.git
synced 2024-11-18 21:43:58 +01:00
97fff61012
The `qsort()` function is not guaranteed to be stable, i.e. it does not promise to maintain the order of items it is told to consider equal. In contrast, the `git_sort()` function we carry in `compat/qsort.c` _is_ stable, by virtue of implementing a merge sort algorithm. In preparation for using a stable sort in Git's rename detection, move the stable sort into `libgit.a` so that it is compiled in unconditionally, and rename it to `git_stable_qsort()`. Note: this also makes the hack obsolete that was introduced in fe21c6b285d (mingw: reencode environment variables on the fly (UTF-16 <-> UTF-8), 2018-10-30), where we included `compat/qsort.c` directly in `compat/mingw.c` to use the stable sort. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
63 lines
1.2 KiB
C
63 lines
1.2 KiB
C
#include "git-compat-util.h"
|
|
|
|
/*
|
|
* A merge sort implementation, simplified from the qsort implementation
|
|
* by Mike Haertel, which is a part of the GNU C Library.
|
|
*/
|
|
|
|
static void msort_with_tmp(void *b, size_t n, size_t s,
|
|
int (*cmp)(const void *, const void *),
|
|
char *t)
|
|
{
|
|
char *tmp;
|
|
char *b1, *b2;
|
|
size_t n1, n2;
|
|
|
|
if (n <= 1)
|
|
return;
|
|
|
|
n1 = n / 2;
|
|
n2 = n - n1;
|
|
b1 = b;
|
|
b2 = (char *)b + (n1 * s);
|
|
|
|
msort_with_tmp(b1, n1, s, cmp, t);
|
|
msort_with_tmp(b2, n2, s, cmp, t);
|
|
|
|
tmp = t;
|
|
|
|
while (n1 > 0 && n2 > 0) {
|
|
if (cmp(b1, b2) <= 0) {
|
|
memcpy(tmp, b1, s);
|
|
tmp += s;
|
|
b1 += s;
|
|
--n1;
|
|
} else {
|
|
memcpy(tmp, b2, s);
|
|
tmp += s;
|
|
b2 += s;
|
|
--n2;
|
|
}
|
|
}
|
|
if (n1 > 0)
|
|
memcpy(tmp, b1, n1 * s);
|
|
memcpy(b, t, (n - n2) * s);
|
|
}
|
|
|
|
void git_stable_qsort(void *b, size_t n, size_t s,
|
|
int (*cmp)(const void *, const void *))
|
|
{
|
|
const size_t size = st_mult(n, s);
|
|
char buf[1024];
|
|
|
|
if (size < sizeof(buf)) {
|
|
/* The temporary array fits on the small on-stack buffer. */
|
|
msort_with_tmp(b, n, s, cmp, buf);
|
|
} else {
|
|
/* It's somewhat large, so malloc it. */
|
|
char *tmp = xmalloc(size);
|
|
msort_with_tmp(b, n, s, cmp, tmp);
|
|
free(tmp);
|
|
}
|
|
}
|