Added a comment

Author: SakiTakamachi

ext/bcmath/libbcmath/src/compare.c

@@ -45,6 +45,10 @@ bcmath_compare_result _bc_do_compare(bc_num n1, bc_num n2, size_t scale, bool us
 
 	/* First, compare signs. */
 	if (use_sign && n1->n_sign != n2->n_sign) {
+		/*
+		 * scale and n->n_scale differ only in Number objects.
+		 * This happens when explicitly specify the scale in a Number method.
+		 */
 		if ((n1->n_scale > scale || n2->n_scale > scale) &&
 			n1->n_len == 1 && n2->n_len == 1 &&
 			n1->n_value[0] == 0 && n2->n_value[0] == 0 &&