</p>

<pre>
type reader struct {
	buf [bufSize]byte
	r   int
}
</pre>

<p>
Assembly can refer to the size of this struct
as <code>reader__size</code> and the offsets of the two fields
as <code>reader_buf</code> and <code>reader_r</code>.
Hence, if register <code>R1</code> contains a pointer to
a <code>reader</code>, assembly can reference the <code>r</code> field