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

dscho · gitster · commit 97fff6101220 · 2019-10-02T14:44:51.000+09:00
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 fe21c6b (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>
diff --git a/Makefile b/Makefile
@@ -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
diff --git a/compat/mingw.c b/compat/mingw.c
@@ -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++) {
diff --git a/git-compat-util.h b/git-compat-util.h
@@ -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);
diff --git a/stable-qsort.c b/stable-qsort.c
@@ -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];

Original file line number	Diff line number	Diff line change
`@@ -1,4 +1,4 @@`
`1`		`-#include "../git-compat-util.h"`
	`1`	`+#include "git-compat-util.h"`
`2`	`2`
`3`	`3`	`/*`
`4`	`4`	`* 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,`
`44`	`44`	`memcpy(b, t, (n - n2) * s);`
`45`	`45`	`}`
`46`	`46`
`47`		`-void git_qsort(void *b, size_t n, size_t s,`
`48`		`- int (cmp)(const void , const void *))`
	`47`	`+void git_stable_qsort(void *b, size_t n, size_t s,`
	`48`	`+ int (cmp)(const void , const void *))`
`49`	`49`	`{`
`50`	`50`	`const size_t size = st_mult(n, s);`
`51`	`51`	`char buf[1024];`