Commit c20ffa6104cf9797a14cc40dcc963102ef9a98a2
2011-07-01T00:34:23
util: introduce merge sort routine In some cases it's important to preserve order of elements with equal keys (stable sort). qsort(3) doesn't define order of elements with equal keys. git__msort() implements merge sort which is stable sort. Implementation taken from git. Function renamed git_qsort() -> git__msort(). Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
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diff --git a/src/util.c b/src/util.c
index 5b8a136..6bdd2d3 100644
--- a/src/util.c
+++ b/src/util.c
@@ -332,3 +332,67 @@ uint32_t git__hash(const void *key, int len, uint32_t seed)
return h1;
}
#endif
+
+/*
+ * 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);
+}
+
+int git__msort(void *b, size_t n, size_t s,
+ int (*cmp)(const void *, const void *))
+{
+ const size_t size = 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 = git__malloc(size);
+ if (tmp == NULL)
+ return GIT_ENOMEM;
+ msort_with_tmp(b, n, s, cmp, tmp);
+ free(tmp);
+ }
+
+ return GIT_SUCCESS;
+}
diff --git a/src/util.h b/src/util.h
index 0faf7f6..c9ca4de 100644
--- a/src/util.h
+++ b/src/util.h
@@ -118,4 +118,7 @@ extern int git__fnmatch(const char *pattern, const char *name, int flags);
} \
} while (0)
+extern int git__msort(void *b, size_t n, size_t s,
+ int (*cmp)(const void *, const void *));
+
#endif /* INCLUDE_util_h__ */