builtin/repack: replace hard-coded constants

Note that while the error messages here are not translated, the end user
should never see them.  We invoke git pack-objects shortly before both
invocations, so we can be fairly certain that the data we're receiving
is in fact valid.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/repack.c

@@ -235,8 +235,8 @@ static void repack_promisor_objects(const struct pack_objects_args *args,
 	while (strbuf_getline_lf(&line, out) != EOF) {
 		char *promisor_name;
 		int fd;
-		if (line.len != 40)
-			die("repack: Expecting 40 character sha1 lines only from pack-objects.");
+		if (line.len != the_hash_algo->hexsz)
+			die("repack: Expecting full hex object ID lines only from pack-objects.");
 		string_list_append(names, line.buf);
 
 		/*
@@ -407,8 +407,8 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 
 	out = xfdopen(cmd.out, "r");
 	while (strbuf_getline_lf(&line, out) != EOF) {
-		if (line.len != 40)
-			die("repack: Expecting 40 character sha1 lines only from pack-objects.");
+		if (line.len != the_hash_algo->hexsz)
+			die("repack: Expecting full hex object ID lines only from pack-objects.");
 		string_list_append(&names, line.buf);
 	}
 	fclose(out);
@@ -535,14 +535,15 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 	reprepare_packed_git(the_repository);
 
 	if (delete_redundant) {
+		const int hexsz = the_hash_algo->hexsz;
 		int opts = 0;
 		string_list_sort(&names);
 		for_each_string_list_item(item, &existing_packs) {
 			char *sha1;
 			size_t len = strlen(item->string);
-			if (len < 40)
+			if (len < hexsz)
 				continue;
-			sha1 = item->string + len - 40;
+			sha1 = item->string + len - hexsz;
 			if (!string_list_has_string(&names, sha1))
 				remove_redundant_pack(packdir, item->string);
 		}