--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtommath/bn_mp_complement.c	Thu Oct 15 19:55:15 2020 +0800
@@ -0,0 +1,12 @@
+#include "tommath_private.h"
+#ifdef BN_MP_COMPLEMENT_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* b = ~a */
+mp_err mp_complement(const mp_int *a, mp_int *b)
+{
+   mp_err err = mp_neg(a, b);
+   return (err == MP_OKAY) ? mp_sub_d(b, 1uL, b) : err;
+}
+#endif