Reduce integrated LibTomMath size by dropping negative exponent support

Current uses do not require support for negative exponent in exptmod, so we
can save about 1.5 kB in leaving out invmod.

src/tls/libtommath.c

@@ -30,6 +30,9 @@
 #define BN_S_MP_MUL_HIGH_DIGS_C /* Note: #undef in tommath_superclass.h; this
 				 * would require other than mp_reduce */
 
+/* Current uses do not require support for negative exponent in exptmod, so we
+ * can save about 1.5 kB in leaving out invmod. */
+#define LTM_NO_NEG_EXP
 
 /* from tommath.h */
 
@@ -122,16 +125,18 @@ static int mp_mod_2d(mp_int * a, int b, mp_int * c);
 static int mp_div_2d(mp_int * a, int b, mp_int * c, mp_int * d);
 static int mp_init_copy(mp_int * a, mp_int * b);
 static int mp_mul_2d(mp_int * a, int b, mp_int * c);
+#ifndef LTM_NO_NEG_EXP
 static int mp_div_2(mp_int * a, mp_int * b);
+static int mp_invmod(mp_int * a, mp_int * b, mp_int * c);
+static int mp_invmod_slow(mp_int * a, mp_int * b, mp_int * c);
+#endif /* LTM_NO_NEG_EXP */
 static int mp_copy(mp_int * a, mp_int * b);
 static int mp_count_bits(mp_int * a);
 static int mp_div(mp_int * a, mp_int * b, mp_int * c, mp_int * d);
 static int mp_mod(mp_int * a, mp_int * b, mp_int * c);
 static int mp_grow(mp_int * a, int size);
 static int mp_cmp_mag(mp_int * a, mp_int * b);
-static int mp_invmod(mp_int * a, mp_int * b, mp_int * c);
 static int mp_abs(mp_int * a, mp_int * b);
-static int mp_invmod_slow(mp_int * a, mp_int * b, mp_int * c);
 static int mp_sqr(mp_int * a, mp_int * b);
 static int mp_reduce_2k_l(mp_int *a, mp_int *n, mp_int *d);
 static int mp_reduce_2k_setup_l(mp_int *a, mp_int *d);
@@ -546,6 +551,9 @@ static int mp_exptmod (mp_int * G, mp_int * X, mp_int * P, mp_int * Y)
 
   /* if exponent X is negative we have to recurse */
   if (X->sign == MP_NEG) {
+#ifdef LTM_NO_NEG_EXP
+        return MP_VAL;
+#else /* LTM_NO_NEG_EXP */
 #ifdef BN_MP_INVMOD_C
      mp_int tmpG, tmpX;
      int err;
@@ -578,6 +586,7 @@ static int mp_exptmod (mp_int * G, mp_int * X, mp_int * P, mp_int * Y)
      /* no invmod */
      return MP_VAL;
 #endif
+#endif /* LTM_NO_NEG_EXP */
   }
 
 /* modified diminished radix reduction */
@@ -668,6 +677,7 @@ static int mp_cmp_d(mp_int * a, mp_digit b)
 }
 
 
+#ifndef LTM_NO_NEG_EXP
 /* hac 14.61, pp608 */
 static int mp_invmod (mp_int * a, mp_int * b, mp_int * c)
 {
@@ -694,6 +704,7 @@ static int mp_invmod (mp_int * a, mp_int * b, mp_int * c)
 #endif
   return MP_VAL;
 }
+#endif /* LTM_NO_NEG_EXP */
 
 
 /* get the size for an unsigned equivalent */
@@ -704,6 +715,7 @@ static int mp_unsigned_bin_size (mp_int * a)
 }
 
 
+#ifndef LTM_NO_NEG_EXP
 /* hac 14.61, pp608 */
 static int mp_invmod_slow (mp_int * a, mp_int * b, mp_int * c)
 {
@@ -857,6 +869,7 @@ top:
 LBL_ERR:mp_clear_multi (&x, &y, &u, &v, &A, &B, &C, &D, NULL);
   return res;
 }
+#endif /* LTM_NO_NEG_EXP */
 
 
 /* compare maginitude of two ints (unsigned) */
@@ -1264,6 +1277,7 @@ static void mp_set (mp_int * a, mp_digit b)
 }
 
 
+#ifndef LTM_NO_NEG_EXP
 /* b = a/2 */
 static int mp_div_2(mp_int * a, mp_int * b)
 {
@@ -1310,6 +1324,7 @@ static int mp_div_2(mp_int * a, mp_int * b)
   mp_clamp (b);
   return MP_OKAY;
 }
+#endif /* LTM_NO_NEG_EXP */
 
 
 /* shift left by a certain bit count */