pack-write.c: extract 'write_rev_file_order'

Existing callers provide the reverse index code with an array of 'struct
pack_idx_entry *'s, which is then sorted by pack order (comparing the
offsets of each object within the pack).

Prepare for the multi-pack index to write a .rev file by providing a way
to write the reverse index without an array of pack_idx_entry (which the
MIDX code does not have).

Instead, callers can invoke 'write_rev_index_positions()', which takes
an array of uint32_t's. The ith entry in this array specifies the ith
object's (in index order) position within the pack (in pack order).

Expose this new function for use in a later patch, and rewrite the
existing write_rev_file() in terms of this new function.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pack-write.c

@@ -201,21 +201,12 @@ static void write_rev_header(struct hashfile *f)
 }
 
 static void write_rev_index_positions(struct hashfile *f,
-				      struct pack_idx_entry **objects,
+				      uint32_t *pack_order,
 				      uint32_t nr_objects)
 {
-	uint32_t *pack_order;
 	uint32_t i;
-
-	ALLOC_ARRAY(pack_order, nr_objects);
-	for (i = 0; i < nr_objects; i++)
-		pack_order[i] = i;
-	QSORT_S(pack_order, nr_objects, pack_order_cmp, objects);
-
 	for (i = 0; i < nr_objects; i++)
 		hashwrite_be32(f, pack_order[i]);
-
-	free(pack_order);
 }
 
 static void write_rev_trailer(struct hashfile *f, const unsigned char *hash)
@@ -228,6 +219,29 @@ const char *write_rev_file(const char *rev_name,
 			   uint32_t nr_objects,
 			   const unsigned char *hash,
 			   unsigned flags)
+{
+	uint32_t *pack_order;
+	uint32_t i;
+	const char *ret;
+
+	ALLOC_ARRAY(pack_order, nr_objects);
+	for (i = 0; i < nr_objects; i++)
+		pack_order[i] = i;
+	QSORT_S(pack_order, nr_objects, pack_order_cmp, objects);
+
+	ret = write_rev_file_order(rev_name, pack_order, nr_objects, hash,
+				   flags);
+
+	free(pack_order);
+
+	return ret;
+}
+
+const char *write_rev_file_order(const char *rev_name,
+				 uint32_t *pack_order,
+				 uint32_t nr_objects,
+				 const unsigned char *hash,
+				 unsigned flags)
 {
 	struct hashfile *f;
 	int fd;
@@ -262,7 +276,7 @@ const char *write_rev_file(const char *rev_name,
 
 	write_rev_header(f);
 
-	write_rev_index_positions(f, objects, nr_objects);
+	write_rev_index_positions(f, pack_order, nr_objects);
 	write_rev_trailer(f, hash);
 
 	if (rev_name && adjust_shared_perm(rev_name) < 0)

pack.h

@@ -94,6 +94,7 @@ struct ref;
 void write_promisor_file(const char *promisor_name, struct ref **sought, int nr_sought);
 
 const char *write_rev_file(const char *rev_name, struct pack_idx_entry **objects, uint32_t nr_objects, const unsigned char *hash, unsigned flags);
+const char *write_rev_file_order(const char *rev_name, uint32_t *pack_order, uint32_t nr_objects, const unsigned char *hash, unsigned flags);
 
 /*
  * The "hdr" output buffer should be at least this big, which will handle sizes