--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtommath/bn_mp_signed_rsh.c	Thu Oct 15 19:55:15 2020 +0800
@@ -0,0 +1,22 @@
+#include "tommath_private.h"
+#ifdef BN_MP_SIGNED_RSH_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* shift right by a certain bit count with sign extension */
+mp_err mp_signed_rsh(const mp_int *a, int b, mp_int *c)
+{
+   mp_err res;
+   if (a->sign == MP_ZPOS) {
+      return mp_div_2d(a, b, c, NULL);
+   }
+
+   res = mp_add_d(a, 1uL, c);
+   if (res != MP_OKAY) {
+      return res;
+   }
+
+   res = mp_div_2d(c, b, c, NULL);
+   return (res == MP_OKAY) ? mp_sub_d(c, 1uL, c) : res;
+}
+#endif