Use mbedtls_mpi_sint not mbedtls_mpi_uint in mpi_mod_int test
@@ -981,11 +981,21 @@ void mpi_mod_int( char * input_X, char * input_Y,
TEST_EQUAL( Y.n, 1 );
TEST_EQUAL( A.n, 1 );
- /* Convert the MPIs for Y and A to signed mbedtls_mpi_uints */
- mbedtls_mpi_uint y = Y.p[0];
+ /* Convert the MPIs for Y and A to (signed) mbedtls_mpi_sints */
+
+ /* Since we're converting sign+magnitude to two's complement, we lose one
+ * bit of value in the output. This means there are some values we can't
+ * represent, e.g. (hex) -A0000000 on 32-bit systems. These are technically
+ * invalid test cases, so could be considered "won't happen", but they are
+ * easy to test for, and this helps guard against human error. */
+
+ mbedtls_mpi_sint y = (mbedtls_mpi_sint) Y.p[0];
+ TEST_ASSERT( y >= 0 ); /* If y < 0 here, we can't make negative y */
if( Y.s == -1 )
y = -y;
- mbedtls_mpi_uint a = A.p[0];
+
+ mbedtls_mpi_sint a = (mbedtls_mpi_sint) A.p[0];
+ TEST_ASSERT( a >= 0 ); /* Same goes for a */
if( A.s == -1 )
a = -a;
