This is another place where we shouldn't hardcode the
SH1_DIGEST_LENGTH_STRING.  ok?

diff /home/op/w/got
commit - 020f73dba5df9e319726af7526dbb3b478d52b76
path + /home/op/w/got
blob - 070b80df0cce4e90b81489df1c9f71ce5c1c3cc7
file + lib/reference.c
--- lib/reference.c
+++ lib/reference.c
@@ -298,8 +298,10 @@ parse_packed_ref_line(struct got_reference **ref, cons
 {
 	struct got_object_id id;
 	const char *name;
+	size_t idlen;
 
 	*ref = NULL;
+	idlen = got_hash_digest_string_length(algo);
 
 	if (line[0] == '#' || line[0] == '^')
 		return NULL;
@@ -308,11 +310,11 @@ parse_packed_ref_line(struct got_reference **ref, cons
 		return got_error(GOT_ERR_BAD_REF_DATA);
 
 	if (abs_refname) {
-		if (strcmp(line + SHA1_DIGEST_STRING_LENGTH, abs_refname) != 0)
+		if (strcmp(line + idlen, abs_refname) != 0)
 			return NULL;
 		name = abs_refname;
 	} else
-		name = line + SHA1_DIGEST_STRING_LENGTH;
+		name = line + idlen;
 
 	return alloc_ref(ref, name, &id, GOT_REF_IS_PACKED, mtime);
 }