_IO_blen
FREE_BUF (f->_IO_buf_base, _IO_blen (f));
FREE_BUF (fp->_IO_buf_base, _IO_blen (fp));
fp->_freeres_size = _IO_blen (fp);
if (pos >= (_IO_size_t) (_IO_blen (fp) + flush_only))
size_t old_blen = _IO_blen (fp);
if ((_IO_ssize_t) offset <= _IO_blen (fp))
memcpy (newbuf, oldbuf, _IO_blen (fp));
if ((_IO_ssize_t) offset <= _IO_blen (fp))