base = read_sha1_file(base_sha1, type, &base_size);
if (!base)
die("failed to read delta-pack base object %s", sha1_to_hex(base_sha1));
base = read_sha1_file(base_sha1, type, &base_size);
if (!base)
die("failed to read delta-pack base object %s", sha1_to_hex(base_sha1));