Introduce "base_name_compare()" helper function

This one compares two pathnames that may be partial basenames, not
full paths. We need to get the path sorting right, since a directory
name will sort as if it had the final '/' at the end.

cache.h

@@ -173,6 +173,7 @@ extern void usage(const char *err);
 extern void die(const char *err, ...);
 extern int error(const char *err, ...);
 
+extern int base_name_compare(const char *name1, int len1, int mode1, const char *name2, int len2, int mode2);
 extern int cache_name_compare(const char *name1, int len1, const char *name2, int len2);
 
 extern void *read_object_with_reference(const unsigned char *sha1,

read-cache.c

@@ -74,6 +74,25 @@ int ce_match_stat(struct cache_entry *ce, struct stat *st)
 	return changed;
 }
 
+int base_name_compare(const char *name1, int len1, int mode1,
+		      const char *name2, int len2, int mode2)
+{
+	unsigned char c1, c2;
+	int len = len1 < len2 ? len1 : len2;
+	int cmp;
+
+	cmp = memcmp(name1, name2, len);
+	if (cmp)
+		return cmp;
+	c1 = name1[len];
+	c2 = name2[len];
+	if (!c1 && S_ISDIR(mode1))
+		c1 = '/';
+	if (!c2 && S_ISDIR(mode2))
+		c2 = '/';
+	return (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
+}
+
 int cache_name_compare(const char *name1, int flags1, const char *name2, int flags2)
 {
 	int len1 = flags1 & CE_NAMEMASK;