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Move git_sort(), a stable sort, into into libgit.a

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
fe21c6b285 (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>
tags/v2.24.0-rc0
Johannes Schindelin Junio C Hamano 1 month ago
parent
commit
97fff61012
4 changed files with 13 additions and 15 deletions
  1. +1
    -1
      Makefile
  2. +3
    -8
      compat/mingw.c
  3. +6
    -3
      git-compat-util.h
  4. +3
    -3
      stable-qsort.c

+ 1
- 1
Makefile View File

@@ -983,6 +983,7 @@ LIB_OBJS += shallow.o
LIB_OBJS += sideband.o
LIB_OBJS += sigchain.o
LIB_OBJS += split-index.o
LIB_OBJS += stable-qsort.o
LIB_OBJS += strbuf.o
LIB_OBJS += streaming.o
LIB_OBJS += string-list.o
@@ -1714,7 +1715,6 @@ ifdef NO_GETPAGESIZE
endif
ifdef INTERNAL_QSORT
COMPAT_CFLAGS += -DINTERNAL_QSORT
COMPAT_OBJS += compat/qsort.o
endif
ifdef HAVE_ISO_QSORT_S
COMPAT_CFLAGS += -DHAVE_ISO_QSORT_S


+ 3
- 8
compat/mingw.c View File

@@ -1229,11 +1229,6 @@ static int wenvcmp(const void *a, const void *b)
return _wcsnicmp(p, q, p_len);
}

/* We need a stable sort to convert the environment between UTF-16 <-> UTF-8 */
#ifndef INTERNAL_QSORT
#include "qsort.c"
#endif

/*
* Build an environment block combining the inherited environment
* merged with the given list of settings.
@@ -1272,8 +1267,8 @@ static wchar_t *make_environment_block(char **deltaenv)

/*
* If there is a deltaenv, let's accumulate all keys into `array`,
* sort them using the stable git_qsort() and then copy, skipping
* duplicate keys
* sort them using the stable git_stable_qsort() and then copy,
* skipping duplicate keys
*/
for (p = wenv; p && *p; ) {
ALLOC_GROW(array, nr + 1, alloc);
@@ -1296,7 +1291,7 @@ static wchar_t *make_environment_block(char **deltaenv)
p += wlen + 1;
}

git_qsort(array, nr, sizeof(*array), wenvcmp);
git_stable_qsort(array, nr, sizeof(*array), wenvcmp);
ALLOC_ARRAY(result, size + delta_size);

for (p = result, i = 0; i < nr; i++) {


+ 6
- 3
git-compat-util.h View File

@@ -1094,10 +1094,10 @@ static inline int strtol_i(char const *s, int base, int *result)
return 0;
}

void git_stable_qsort(void *base, size_t nmemb, size_t size,
int(*compar)(const void *, const void *));
#ifdef INTERNAL_QSORT
void git_qsort(void *base, size_t nmemb, size_t size,
int(*compar)(const void *, const void *));
#define qsort git_qsort
#define qsort git_stable_qsort
#endif

#define QSORT(base, n, compar) sane_qsort((base), (n), sizeof(*(base)), compar)
@@ -1108,6 +1108,9 @@ static inline void sane_qsort(void *base, size_t nmemb, size_t size,
qsort(base, nmemb, size, compar);
}

#define STABLE_QSORT(base, n, compar) \
git_stable_qsort((base), (n), sizeof(*(base)), compar)

#ifndef HAVE_ISO_QSORT_S
int git_qsort_s(void *base, size_t nmemb, size_t size,
int (*compar)(const void *, const void *, void *), void *ctx);


compat/qsort.c → stable-qsort.c View File

@@ -1,4 +1,4 @@
#include "../git-compat-util.h"
#include "git-compat-util.h"

/*
* A merge sort implementation, simplified from the qsort implementation
@@ -44,8 +44,8 @@ static void msort_with_tmp(void *b, size_t n, size_t s,
memcpy(b, t, (n - n2) * s);
}

void git_qsort(void *b, size_t n, size_t s,
int (*cmp)(const void *, const void *))
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];

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