alloc: factor out commit index

We keep a static counter to set the commit index on newly
allocated objects. However, since we also need to set the
index on any_objects which are converted to commits, let's
make the counter available as a public function.

While we're moving it, let's make sure the counter is
allocated as an unsigned integer to match the index field in
"struct commit".

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

alloc.c

@@ -82,12 +82,17 @@ void *alloc_object_node(void)
 
 static struct alloc_state commit_state;
 
+unsigned int alloc_commit_index(void)
+{
+	static unsigned int count;
+	return count++;
+}
+
 void *alloc_commit_node(void)
 {
-	static int commit_count;
 	struct commit *c = alloc_node(&commit_state, sizeof(struct commit));
 	c->object.type = OBJ_COMMIT;
-	c->index = commit_count++;
+	c->index = alloc_commit_index();
 	return c;
 }
 

cache.h

@@ -1376,6 +1376,7 @@ extern void *alloc_commit_node(void);
 extern void *alloc_tag_node(void);
 extern void *alloc_object_node(void);
 extern void alloc_report(void);
+extern unsigned int alloc_commit_index(void);
 
 /* trace.c */
 __attribute__((format (printf, 1, 2)))