--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtommath/bn_s_mp_reverse.c	Thu Oct 15 19:55:15 2020 +0800
@@ -0,0 +1,22 @@
+#include "tommath_private.h"
+#ifdef BN_S_MP_REVERSE_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* reverse an array, used for radix code */
+void s_mp_reverse(unsigned char *s, size_t len)
+{
+   size_t   ix, iy;
+   unsigned char t;
+
+   ix = 0u;
+   iy = len - 1u;
+   while (ix < iy) {
+      t     = s[ix];
+      s[ix] = s[iy];
+      s[iy] = t;
+      ++ix;
+      --iy;
+   }
+}
+#endif