+ const char *a_prefix, *b_prefix;
+
+ diff_set_mnemonic_prefix(o, "a/", "b/");
+ if (DIFF_OPT_TST(o, REVERSE_DIFF)) {
+ a_prefix = o->b_prefix;
+ b_prefix = o->a_prefix;
+ } else {
+ a_prefix = o->a_prefix;
+ b_prefix = o->b_prefix;
+ }
+
+ /* Never use a non-valid filename anywhere if at all possible */
+ name_a = DIFF_FILE_VALID(one) ? name_a : name_b;
+ name_b = DIFF_FILE_VALID(two) ? name_b : name_a;