--- a/libtommath/bn_s_mp_add.c	Wed Feb 28 22:11:39 2018 +0800
+++ b/libtommath/bn_s_mp_add.c	Thu Oct 15 19:55:15 2020 +0800
@@ -1,109 +1,91 @@
-#include <tommath_private.h>
+#include "tommath_private.h"
 #ifdef BN_S_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 */
 
 /* low level addition, based on HAC pp.594, Algorithm 14.7 */
-int
-s_mp_add (mp_int * a, mp_int * b, mp_int * c)
+mp_err s_mp_add(const mp_int *a, const mp_int *b, mp_int *c)
 {
-  mp_int *x;
-  int     olduse, res, min, max;
+   const mp_int *x;
+   mp_err err;
+   int     olduse, min, max;
 
-  /* find sizes, we let |a| <= |b| which means we have to sort
-   * them.  "x" will point to the input with the most digits
-   */
-  if (a->used > b->used) {
-    min = b->used;
-    max = a->used;
-    x = a;
-  } else {
-    min = a->used;
-    max = b->used;
-    x = b;
-  }
+   /* find sizes, we let |a| <= |b| which means we have to sort
+    * them.  "x" will point to the input with the most digits
+    */
+   if (a->used > b->used) {
+      min = b->used;
+      max = a->used;
+      x = a;
+   } else {
+      min = a->used;
+      max = b->used;
+      x = b;
+   }
 
-  /* init result */
-  if (c->alloc < (max + 1)) {
-    if ((res = mp_grow (c, max + 1)) != MP_OKAY) {
-      return res;
-    }
-  }
+   /* init result */
+   if (c->alloc < (max + 1)) {
+      if ((err = mp_grow(c, max + 1)) != MP_OKAY) {
+         return err;
+      }
+   }
 
-  /* get old used digit count and set new one */
-  olduse = c->used;
-  c->used = max + 1;
+   /* get old used digit count and set new one */
+   olduse = c->used;
+   c->used = max + 1;
 
-  {
-    mp_digit u, *tmpa, *tmpb, *tmpc;
-    int i;
+   {
+      mp_digit u, *tmpa, *tmpb, *tmpc;
+      int i;
 
-    /* alias for digit pointers */
+      /* alias for digit pointers */
 
-    /* first input */
-    tmpa = a->dp;
+      /* first input */
+      tmpa = a->dp;
 
-    /* second input */
-    tmpb = b->dp;
+      /* second input */
+      tmpb = b->dp;
 
-    /* destination */
-    tmpc = c->dp;
+      /* destination */
+      tmpc = c->dp;
 
-    /* zero the carry */
-    u = 0;
-    for (i = 0; i < min; i++) {
-      /* Compute the sum at one digit, T[i] = A[i] + B[i] + U */
-      *tmpc = *tmpa++ + *tmpb++ + u;
+      /* zero the carry */
+      u = 0;
+      for (i = 0; i < min; i++) {
+         /* Compute the sum at one digit, T[i] = A[i] + B[i] + U */
+         *tmpc = *tmpa++ + *tmpb++ + u;
 
-      /* U = carry bit of T[i] */
-      u = *tmpc >> ((mp_digit)DIGIT_BIT);
+         /* U = carry bit of T[i] */
+         u = *tmpc >> (mp_digit)MP_DIGIT_BIT;
 
-      /* take away carry bit from T[i] */
-      *tmpc++ &= MP_MASK;
-    }
+         /* take away carry bit from T[i] */
+         *tmpc++ &= MP_MASK;
+      }
 
-    /* now copy higher words if any, that is in A+B 
-     * if A or B has more digits add those in 
-     */
-    if (min != max) {
-      for (; i < max; i++) {
-        /* T[i] = X[i] + U */
-        *tmpc = x->dp[i] + u;
+      /* now copy higher words if any, that is in A+B
+       * if A or B has more digits add those in
+       */
+      if (min != max) {
+         for (; i < max; i++) {
+            /* T[i] = X[i] + U */
+            *tmpc = x->dp[i] + u;
 
-        /* U = carry bit of T[i] */
-        u = *tmpc >> ((mp_digit)DIGIT_BIT);
+            /* U = carry bit of T[i] */
+            u = *tmpc >> (mp_digit)MP_DIGIT_BIT;
 
-        /* take away carry bit from T[i] */
-        *tmpc++ &= MP_MASK;
+            /* take away carry bit from T[i] */
+            *tmpc++ &= MP_MASK;
+         }
       }
-    }
 
-    /* add carry */
-    *tmpc++ = u;
+      /* add carry */
+      *tmpc++ = u;
 
-    /* clear digits above oldused */
-    for (i = c->used; i < olduse; i++) {
-      *tmpc++ = 0;
-    }
-  }
+      /* clear digits above oldused */
+      MP_ZERO_DIGITS(tmpc, olduse - c->used);
+   }
 
-  mp_clamp (c);
-  return MP_OKAY;
+   mp_clamp(c);
+   return MP_OKAY;
 }
 #endif
-
-/* ref:         $Format:%D$ */
-/* git commit:  $Format:%H$ */
-/* commit time: $Format:%ai$ */