optimize verify-pack a bit

Using find_pack_entry_one() to get object offsets is rather suboptimal
when nth_packed_object_offset() can be used directly.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -712,6 +712,7 @@ extern void close_pack_windows(struct packed_git *);
 extern void unuse_pack(struct pack_window **);
 extern struct packed_git *add_packed_git(const char *, int, int);
 extern const unsigned char *nth_packed_object_sha1(struct packed_git *, uint32_t);
+extern off_t nth_packed_object_offset(const struct packed_git *, uint32_t);
 extern off_t find_pack_entry_one(const unsigned char *, struct packed_git *);
 extern void *unpack_entry(struct packed_git *, off_t, enum object_type *, unsigned long *);
 extern unsigned long unpack_object_header_gently(const unsigned char *buf, unsigned long len, enum object_type *type, unsigned long *sizep);

pack-check.c

@@ -67,9 +67,7 @@ static int verify_packfile(struct packed_git *p,
 		entries[i].sha1 = nth_packed_object_sha1(p, i);
 		if (!entries[i].sha1)
 			die("internal error pack-check nth-packed-object");
-		entries[i].offset = find_pack_entry_one(entries[i].sha1, p);
-		if (!entries[i].offset)
-			die("internal error pack-check find-pack-entry-one");
+		entries[i].offset = nth_packed_object_offset(p, i);
 	}
 	qsort(entries, nr_objects, sizeof(*entries), compare_entries);
 

sha1_file.c

@@ -1714,7 +1714,7 @@ const unsigned char *nth_packed_object_sha1(struct packed_git *p,
 	}
 }
 
-static off_t nth_packed_object_offset(const struct packed_git *p, uint32_t n)
+off_t nth_packed_object_offset(const struct packed_git *p, uint32_t n)
 {
 	const unsigned char *index = p->index_data;
 	index += 4 * 256;