Avoid in-out length parameter in bignum
diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index 0dfe22e..d03b983 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -324,17 +324,19 @@
*
* \param X Source MPI
* \param radix Output numeric base
- * \param s String buffer
- * \param slen String buffer size
+ * \param buf Buffer to write the string to
+ * \param buflen Length of buf
+ * \param olen Length of the string written, including final NUL byte
*
* \return 0 if successful, or a MBEDTLS_ERR_MPI_XXX error code.
- * *slen is always updated to reflect the amount
+ * *olen is always updated to reflect the amount
* of data that has (or would have) been written.
*
- * \note Call this function with *slen = 0 to obtain the
- * minimum required buffer size in *slen.
+ * \note Call this function with buflen = 0 to obtain the
+ * minimum required buffer size in *olen.
*/
-int mbedtls_mpi_write_string( const mbedtls_mpi *X, int radix, char *s, size_t *slen );
+int mbedtls_mpi_write_string( const mbedtls_mpi *X, int radix,
+ char *buf, size_t buflen, size_t *olen );
#if defined(MBEDTLS_FS_IO)
/**