Improve testing of mbedtls_mpi_gcd() and mbedtls_mpi_inv_mod()
Signed-off-by: Felix Conway <felix.conway@arm.com>
diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index 1e1c063..ed0c4e7 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -988,10 +988,13 @@
* \brief Compute the modular inverse: X = A^-1 mod N
*
* \param X The destination MPI. This must point to an initialized MPI.
+ * The value returned on success will be between [1, N-1].
* \param A The MPI to calculate the modular inverse of. This must point
- * to an initialized MPI.
+ * to an initialized MPI. This value can be negative, in which
+ * case a positive answer will still be returned in \p X.
* \param N The base of the modular inversion. This must point to an
- * initialized MPI.
+ * initialized MPI. If this points to the same MPI as \p X,
+ * then the value returned in \p X will be incorrect.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_ALLOC_FAILED if a memory allocation failed.