Reworked NO_FALLBACK logic according to review feedback

Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
diff --git a/library/ecp.c b/library/ecp.c
index 044712f..3b68e8e 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -1302,11 +1302,6 @@
  */
 static int ecp_normalize_jac( const mbedtls_ecp_group *grp, mbedtls_ecp_point *pt )
 {
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_JAC_ALT)
-    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
-    mbedtls_mpi Zi, ZZi;
-#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_JAC_ALT) */
-
     if( mbedtls_mpi_cmp_int( &pt->Z, 0 ) == 0 )
         return( 0 );
 
@@ -1314,7 +1309,12 @@
     if( mbedtls_internal_ecp_grp_capable( grp ) )
         return( mbedtls_internal_ecp_normalize_jac( grp, pt ) );
 #endif /* MBEDTLS_ECP_NORMALIZE_JAC_ALT */
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_JAC_ALT)
+
+#if defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_NORMALIZE_JAC_ALT)
+    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
+#else
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    mbedtls_mpi Zi, ZZi;
     mbedtls_mpi_init( &Zi ); mbedtls_mpi_init( &ZZi );
 
     /*
@@ -1340,9 +1340,7 @@
     mbedtls_mpi_free( &Zi ); mbedtls_mpi_free( &ZZi );
 
     return( ret );
-#else /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_JAC_ALT) */
-    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
-#endif /* defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_NORMALIZE_JAC_ALT) */
+#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_JAC_ALT) */
 }
 
 /*
@@ -1359,12 +1357,6 @@
 static int ecp_normalize_jac_many( const mbedtls_ecp_group *grp,
                                    mbedtls_ecp_point *T[], size_t T_size )
 {
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_JAC_MANY_ALT)
-    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
-    size_t i;
-    mbedtls_mpi *c, u, Zi, ZZi;
-#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_JAC_MANY_ALT) */
-
     if( T_size < 2 )
         return( ecp_normalize_jac( grp, *T ) );
 
@@ -1373,7 +1365,13 @@
         return( mbedtls_internal_ecp_normalize_jac_many( grp, T, T_size ) );
 #endif
 
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_JAC_MANY_ALT)
+#if defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_NORMALIZE_JAC_MANY_ALT)
+    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
+#else
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    size_t i;
+    mbedtls_mpi *c, u, Zi, ZZi;
+
     if( ( c = mbedtls_calloc( T_size, sizeof( mbedtls_mpi ) ) ) == NULL )
         return( MBEDTLS_ERR_ECP_ALLOC_FAILED );
 
@@ -1441,9 +1439,7 @@
     mbedtls_free( c );
 
     return( ret );
-#else /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_JAC_MANY_ALT) */
-    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
-#endif /* defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_NORMALIZE_JAC_MANY_ALT) */
+#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_JAC_MANY_ALT) */
 }
 
 /*
@@ -1488,11 +1484,6 @@
 static int ecp_double_jac( const mbedtls_ecp_group *grp, mbedtls_ecp_point *R,
                            const mbedtls_ecp_point *P )
 {
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_DOUBLE_JAC_ALT)
-    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
-    mbedtls_mpi M, S, T, U;
-#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_DOUBLE_JAC_ALT) */
-
 #if defined(MBEDTLS_SELF_TEST)
     dbl_count++;
 #endif
@@ -1502,7 +1493,12 @@
         return( mbedtls_internal_ecp_double_jac( grp, R, P ) );
 #endif /* MBEDTLS_ECP_DOUBLE_JAC_ALT */
 
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_DOUBLE_JAC_ALT)
+#if defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_DOUBLE_JAC_ALT)
+    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
+#else
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    mbedtls_mpi M, S, T, U;
+
     mbedtls_mpi_init( &M ); mbedtls_mpi_init( &S ); mbedtls_mpi_init( &T ); mbedtls_mpi_init( &U );
 
     /* Special case for A = -3 */
@@ -1564,9 +1560,7 @@
     mbedtls_mpi_free( &M ); mbedtls_mpi_free( &S ); mbedtls_mpi_free( &T ); mbedtls_mpi_free( &U );
 
     return( ret );
-#else /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_DOUBLE_JAC_ALT) */
-    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
-#endif /* defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_DOUBLE_JAC_ALT) */
+#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_DOUBLE_JAC_ALT) */
 }
 
 /*
@@ -1590,11 +1584,6 @@
 static int ecp_add_mixed( const mbedtls_ecp_group *grp, mbedtls_ecp_point *R,
                           const mbedtls_ecp_point *P, const mbedtls_ecp_point *Q )
 {
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_ADD_MIXED_ALT)
-    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
-    mbedtls_mpi T1, T2, T3, T4, X, Y, Z;
-#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_ADD_MIXED_ALT) */
-
 #if defined(MBEDTLS_SELF_TEST)
     add_count++;
 #endif
@@ -1604,7 +1593,12 @@
         return( mbedtls_internal_ecp_add_mixed( grp, R, P, Q ) );
 #endif /* MBEDTLS_ECP_ADD_MIXED_ALT */
 
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_ADD_MIXED_ALT)
+#if defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_ADD_MIXED_ALT)
+    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
+#else
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    mbedtls_mpi T1, T2, T3, T4, X, Y, Z;
+
     /*
      * Trivial cases: P == 0 or Q == 0 (case 1)
      */
@@ -1669,9 +1663,7 @@
     mbedtls_mpi_free( &X ); mbedtls_mpi_free( &Y ); mbedtls_mpi_free( &Z );
 
     return( ret );
-#else /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_ADD_MIXED_ALT) */
-    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
-#endif /* defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_ADD_MIXED_ALT) */
+#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_ADD_MIXED_ALT) */
 }
 
 /*
@@ -1684,20 +1676,19 @@
 static int ecp_randomize_jac( const mbedtls_ecp_group *grp, mbedtls_ecp_point *pt,
                 int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
 {
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_RANDOMIZE_JAC_ALT)
-    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
-    mbedtls_mpi l, ll;
-    size_t p_size;
-    int count = 0;
-#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_RANDOMIZE_JAC_ALT) */
-
 #if defined(MBEDTLS_ECP_RANDOMIZE_JAC_ALT)
     if( mbedtls_internal_ecp_grp_capable( grp ) )
         return( mbedtls_internal_ecp_randomize_jac( grp, pt, f_rng, p_rng ) );
 #endif /* MBEDTLS_ECP_RANDOMIZE_JAC_ALT */
 
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_RANDOMIZE_JAC_ALT)
-    p_size = ( grp->pbits + 7 ) / 8;
+#if defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_RANDOMIZE_JAC_ALT)
+    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
+#else
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    mbedtls_mpi l, ll;
+    int count = 0;
+    size_t p_size = ( grp->pbits + 7 ) / 8;
+
     mbedtls_mpi_init( &l ); mbedtls_mpi_init( &ll );
 
     /* Generate l such that 1 < l < p */
@@ -1731,9 +1722,7 @@
     mbedtls_mpi_free( &l ); mbedtls_mpi_free( &ll );
 
     return( ret );
-#else /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_RANDOMIZE_JAC_ALT) */
-    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
-#endif /* defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_RANDOMIZE_JAC_ALT) */
+#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_RANDOMIZE_JAC_ALT) */
 }
 
 /*
@@ -2442,25 +2431,22 @@
  */
 static int ecp_normalize_mxz( const mbedtls_ecp_group *grp, mbedtls_ecp_point *P )
 {
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_MXZ_ALT)
-    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
-#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_MXZ_ALT) */
-
 #if defined(MBEDTLS_ECP_NORMALIZE_MXZ_ALT)
     if( mbedtls_internal_ecp_grp_capable( grp ) )
         return( mbedtls_internal_ecp_normalize_mxz( grp, P ) );
 #endif /* MBEDTLS_ECP_NORMALIZE_MXZ_ALT */
 
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_MXZ_ALT)
+#if defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_NORMALIZE_MXZ_ALT)
+    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
+#else
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( &P->Z, &P->Z, &grp->P ) );
     MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mod( grp, &P->X, &P->X, &P->Z ) );
     MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &P->Z, 1 ) );
 
 cleanup:
     return( ret );
-#else /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_MXZ_ALT) */
-    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
-#endif /* defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_NORMALIZE_MXZ_ALT) */
+#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_NORMALIZE_MXZ_ALT) */
 }
 
 /*
@@ -2474,20 +2460,18 @@
 static int ecp_randomize_mxz( const mbedtls_ecp_group *grp, mbedtls_ecp_point *P,
                 int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
 {
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_RANDOMIZE_MXZ_ALT)
-    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
-    mbedtls_mpi l;
-    size_t p_size;
-    int count = 0;
-#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_RANDOMIZE_MXZ_ALT) */
-
 #if defined(MBEDTLS_ECP_RANDOMIZE_MXZ_ALT)
     if( mbedtls_internal_ecp_grp_capable( grp ) )
         return( mbedtls_internal_ecp_randomize_mxz( grp, P, f_rng, p_rng );
 #endif /* MBEDTLS_ECP_RANDOMIZE_MXZ_ALT */
 
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_RANDOMIZE_MXZ_ALT)
-    p_size = ( grp->pbits + 7 ) / 8;
+#if defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_RANDOMIZE_MXZ_ALT)
+    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
+#else
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    mbedtls_mpi l;
+    int count = 0;
+    size_t p_size = ( grp->pbits + 7 ) / 8;
     mbedtls_mpi_init( &l );
 
     /* Generate l such that 1 < l < p */
@@ -2513,9 +2497,7 @@
     mbedtls_mpi_free( &l );
 
     return( ret );
-#else /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_RANDOMIZE_MXZ_ALT) */
-    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
-#endif /* defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_RANDOMIZE_MXZ_ALT) */
+#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_RANDOMIZE_MXZ_ALT) */
 }
 
 /*
@@ -2538,17 +2520,17 @@
                                const mbedtls_ecp_point *P, const mbedtls_ecp_point *Q,
                                const mbedtls_mpi *d )
 {
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_DOUBLE_ADD_MXZ_ALT)
-    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
-    mbedtls_mpi A, AA, B, BB, E, C, D, DA, CB;
-#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_DOUBLE_ADD_MXZ_ALT) */
-
 #if defined(MBEDTLS_ECP_DOUBLE_ADD_MXZ_ALT)
     if( mbedtls_internal_ecp_grp_capable( grp ) )
         return( mbedtls_internal_ecp_double_add_mxz( grp, R, S, P, Q, d ) );
 #endif /* MBEDTLS_ECP_DOUBLE_ADD_MXZ_ALT */
 
-#if !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_DOUBLE_ADD_MXZ_ALT)
+#if defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_DOUBLE_ADD_MXZ_ALT)
+    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
+#else
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    mbedtls_mpi A, AA, B, BB, E, C, D, DA, CB;
+
     mbedtls_mpi_init( &A ); mbedtls_mpi_init( &AA ); mbedtls_mpi_init( &B );
     mbedtls_mpi_init( &BB ); mbedtls_mpi_init( &E ); mbedtls_mpi_init( &C );
     mbedtls_mpi_init( &D ); mbedtls_mpi_init( &DA ); mbedtls_mpi_init( &CB );
@@ -2578,9 +2560,7 @@
     mbedtls_mpi_free( &D ); mbedtls_mpi_free( &DA ); mbedtls_mpi_free( &CB );
 
     return( ret );
-#else /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_DOUBLE_ADD_MXZ_ALT) */
-    return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
-#endif /* defined(MBEDTLS_ECP_NO_FALLBACK) && defined(MBEDTLS_ECP_DOUBLE_ADD_MXZ_ALT) */
+#endif /* !defined(MBEDTLS_ECP_NO_FALLBACK) || !defined(MBEDTLS_ECP_DOUBLE_ADD_MXZ_ALT) */
 }
 
 /*