--- a/libtommath/bn_mp_add.c	Wed Feb 28 22:11:39 2018 +0800
+++ b/libtommath/bn_mp_add.c	Thu Oct 15 19:55:15 2020 +0800
@@ -1,53 +1,38 @@
-#include <tommath_private.h>
+#include "tommath_private.h"
 #ifdef BN_MP_ADD_C
-/* LibTomMath, multiple-precision integer library -- Tom St Denis
- *
- * LibTomMath is a library that provides multiple-precision
- * integer arithmetic as well as number theoretic functionality.
- *
- * The library was designed directly after the MPI library by
- * Michael Fromberger but has been written from scratch with
- * additional optimizations in place.
- *
- * The library is free for all purposes without any express
- * guarantee it works.
- *
- * Tom St Denis, [email protected], http://libtom.org
- */
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
 
 /* high level addition (handles signs) */
-int mp_add (mp_int * a, mp_int * b, mp_int * c)
+mp_err mp_add(const mp_int *a, const mp_int *b, mp_int *c)
 {
-  int     sa, sb, res;
+   mp_sign sa, sb;
+   mp_err err;
 
-  /* get sign of both inputs */
-  sa = a->sign;
-  sb = b->sign;
+   /* get sign of both inputs */
+   sa = a->sign;
+   sb = b->sign;
 
-  /* handle two cases, not four */
-  if (sa == sb) {
-    /* both positive or both negative */
-    /* add their magnitudes, copy the sign */
-    c->sign = sa;
-    res = s_mp_add (a, b, c);
-  } else {
-    /* one positive, the other negative */
-    /* subtract the one with the greater magnitude from */
-    /* the one of the lesser magnitude.  The result gets */
-    /* the sign of the one with the greater magnitude. */
-    if (mp_cmp_mag (a, b) == MP_LT) {
-      c->sign = sb;
-      res = s_mp_sub (b, a, c);
-    } else {
+   /* handle two cases, not four */
+   if (sa == sb) {
+      /* both positive or both negative */
+      /* add their magnitudes, copy the sign */
       c->sign = sa;
-      res = s_mp_sub (a, b, c);
-    }
-  }
-  return res;
+      err = s_mp_add(a, b, c);
+   } else {
+      /* one positive, the other negative */
+      /* subtract the one with the greater magnitude from */
+      /* the one of the lesser magnitude.  The result gets */
+      /* the sign of the one with the greater magnitude. */
+      if (mp_cmp_mag(a, b) == MP_LT) {
+         c->sign = sb;
+         err = s_mp_sub(b, a, c);
+      } else {
+         c->sign = sa;
+         err = s_mp_sub(a, b, c);
+      }
+   }
+   return err;
 }
 
 #endif
-
-/* ref:         $Format:%D$ */
-/* git commit:  $Format:%H$ */
-/* commit time: $Format:%ai$ */