--- a/libtommath/bn_mp_exptmod.c	Tue May 26 23:27:26 2020 +0800
+++ b/libtommath/bn_mp_exptmod.c	Tue May 26 17:36:47 2020 +0200
@@ -1,24 +1,14 @@
 #include "tommath_private.h"
 #ifdef BN_MP_EXPTMOD_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.
- *
- * SPDX-License-Identifier: Unlicense
- */
-
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
 
 /* this is a shell function that calls either the normal or Montgomery
  * exptmod functions.  Originally the call to the montgomery code was
  * embedded in the normal function but that wasted alot of stack space
  * for nothing (since 99% of the time the Montgomery code would be called)
  */
-int mp_exptmod(const mp_int *G, const mp_int *X, const mp_int *P, mp_int *Y)
+mp_err mp_exptmod(const mp_int *G, const mp_int *X, const mp_int *P, mp_int *Y)
 {
    int dr;
 
@@ -29,81 +19,58 @@
 
    /* if exponent X is negative we have to recurse */
    if (X->sign == MP_NEG) {
-#ifdef BN_MP_INVMOD_C
       mp_int tmpG, tmpX;
-      int err;
+      mp_err err;
 
-      /* first compute 1/G mod P */
-      if ((err = mp_init(&tmpG)) != MP_OKAY) {
-         return err;
+      if (!MP_HAS(MP_INVMOD)) {
+         return MP_VAL;
       }
-      if ((err = mp_invmod(G, P, &tmpG)) != MP_OKAY) {
-         mp_clear(&tmpG);
+
+      if ((err = mp_init_multi(&tmpG, &tmpX, NULL)) != MP_OKAY) {
          return err;
       }
 
+      /* first compute 1/G mod P */
+      if ((err = mp_invmod(G, P, &tmpG)) != MP_OKAY) {
+         goto LBL_ERR;
+      }
+
       /* now get |X| */
-      if ((err = mp_init(&tmpX)) != MP_OKAY) {
-         mp_clear(&tmpG);
-         return err;
-      }
       if ((err = mp_abs(X, &tmpX)) != MP_OKAY) {
-         mp_clear_multi(&tmpG, &tmpX, NULL);
-         return err;
+         goto LBL_ERR;
       }
 
       /* and now compute (1/G)**|X| instead of G**X [X < 0] */
       err = mp_exptmod(&tmpG, &tmpX, P, Y);
+LBL_ERR:
       mp_clear_multi(&tmpG, &tmpX, NULL);
       return err;
-#else
-      /* no invmod */
-      return MP_VAL;
-#endif
    }
 
    /* modified diminished radix reduction */
-#if defined(BN_MP_REDUCE_IS_2K_L_C) && defined(BN_MP_REDUCE_2K_L_C) && defined(BN_S_MP_EXPTMOD_C)
-   if (mp_reduce_is_2k_l(P) == MP_YES) {
+   if (MP_HAS(MP_REDUCE_IS_2K_L) && MP_HAS(MP_REDUCE_2K_L) && MP_HAS(S_MP_EXPTMOD) &&
+       (mp_reduce_is_2k_l(P) == MP_YES)) {
       return s_mp_exptmod(G, X, P, Y, 1);
    }
-#endif
+
+   /* is it a DR modulus? default to no */
+   dr = (MP_HAS(MP_DR_IS_MODULUS) && (mp_dr_is_modulus(P) == MP_YES)) ? 1 : 0;
 
-#ifdef BN_MP_DR_IS_MODULUS_C
-   /* is it a DR modulus? */
-   dr = mp_dr_is_modulus(P);
-#else
-   /* default to no */
-   dr = 0;
-#endif
-
-#ifdef BN_MP_REDUCE_IS_2K_C
    /* if not, is it a unrestricted DR modulus? */
-   if (dr == 0) {
-      dr = mp_reduce_is_2k(P) << 1;
+   if (MP_HAS(MP_REDUCE_IS_2K) && (dr == 0)) {
+      dr = (mp_reduce_is_2k(P) == MP_YES) ? 2 : 0;
    }
-#endif
 
    /* if the modulus is odd or dr != 0 use the montgomery method */
-#ifdef BN_MP_EXPTMOD_FAST_C
-   if ((mp_isodd(P) == MP_YES) || (dr !=  0)) {
-      return mp_exptmod_fast(G, X, P, Y, dr);
-   } else {
-#endif
-#ifdef BN_S_MP_EXPTMOD_C
+   if (MP_HAS(S_MP_EXPTMOD_FAST) && (MP_IS_ODD(P) || (dr != 0))) {
+      return s_mp_exptmod_fast(G, X, P, Y, dr);
+   } else if (MP_HAS(S_MP_EXPTMOD)) {
       /* otherwise use the generic Barrett reduction technique */
       return s_mp_exptmod(G, X, P, Y, 0);
-#else
+   } else {
       /* no exptmod for evens */
       return MP_VAL;
-#endif
-#ifdef BN_MP_EXPTMOD_FAST_C
    }
-#endif
 }
 
 #endif
-
-/* ref:         HEAD -> master, tag: v1.1.0 */
-/* git commit:  08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
-/* commit time: 2019-01-28 20:32:32 +0100 */