+       <entry><function>hostmask</function>(<type>inet</type>)</entry>
+       <entry><type>inet</type></entry>
+       <entry>construct hostmask for network</entry>
+       <entry><literal>hostmask('192.168.23.20/30')</literal></entry>
+       <entry><literal>0.0.0.3</literal></entry>

Greg Wickham