Mention that mpi_fill_random interprets PRNG output as big-endian
diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index 1a5b4b6..030982d 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -648,6 +648,10 @@
*
* \return 0 if successful,
* MBEDTLS_ERR_MPI_ALLOC_FAILED if memory allocation failed
+ *
+ * \note The bytes obtained from the PRNG are interpreted
+ * as a big-endian representation of an MPI; this can
+ * be relevant in applications like deterministic ECDSA.
*/
int mbedtls_mpi_fill_random( mbedtls_mpi *X, size_t size,
int (*f_rng)(void *, unsigned char *, size_t),