</p>

<pre>
const (
	bit0, mask0 = 1 &lt;&lt; iota, 1&lt;&lt;iota - 1  // bit0 == 1, mask0 == 0  (iota == 0)
	bit1, mask1                           // bit1 == 2, mask1 == 1  (iota == 1)
	_, _                                  //                        (iota == 2, unused)
	bit3, mask3                           // bit3 == 8, mask3 == 7  (iota == 3)
)
</pre>

<p>

and declares <code>runtime·tlsoffset</code>, a 4-byte, implicitly zeroed variable that
contains no pointers.
</p>

<p>
There may be one or two arguments to the directives.
If there are two, the first is a bit mask of flags,
which can be written as numeric expressions, added or or-ed together,
or can be set symbolically for easier absorption by a human.

</p>

<pre>
const (
	bit0, mask0 = 1 &lt;&lt; iota, 1&lt;&lt;iota - 1  // bit0 == 1, mask0 == 0  (iota == 0)
	bit1, mask1                           // bit1 == 2, mask1 == 1  (iota == 1)
	_, _                                  //                        (iota == 2, unused)
	bit3, mask3                           // bit3 == 8, mask3 == 7  (iota == 3)
)
</pre>

<p>