Crc32DualFixup
The Crc32DualFixup will produce a CRC-32 using data from two elements.
Examples
<Block name="Header">
<!-- .... -->
<Number size="32">
<Fixup class="Crc32DualFixup">
<Param name="ref1" value="Header" />
<Param name="ref2" value="Data" />
</Fixup>
</Number>
</Block>
<Blob name="Data" />


