Doing math on multiple datasources and graphing result

I am trying to figure out if Cricket can do some math on multiple 
datasources and somehow graph the result along with other datasources 
in a single graph.

Let's say part of my config file looks like this:

datasource      linkByteCount
         ds-source   =   snmp://%snmp%/linkByteCount.%inst%
 	desc        =   "Lower 32 bits of byte count"

datasource      linkByteCountHi
         ds-source   =   snmp://%snmp%/linkByteCountHi.%inst%
         desc        =   "Upper 32 bits of byte count"

datasource      linkReTxByteCount
         ds-source   =   snmp://%snmp%/linkReTxByteCount.%inst%
         desc        =   "Retransmitted Bytes"

Basically, instead of giving me a single 64-bit counter for "byte count", 
the vendor decides to give me only two, 32-bit SNMP mib variables that I 
must combine together to form the 64-bit value.

Ideally, what I'd like to do is something like this in Reverse Polish 
Notation (RPN):

ByteCount = linkByteCountHi,2,32,*,linkByteCount,+

and then create a targetType:

targetType      databytes
   ds  =  "ByteCount, linkReTxByteCount"
   view  =  "Bytes: ByteCount linkReTxByteCount"

and then graph a target with it.  Unfortunately, I am unable to figure out 
how to combine two datasources together with the extra math to 
create a new datasource to make this happen.

I would settle for some RPN work using either "mtargets" or using "scale" 
on the graph, but I haven't been able come up with anything useful.

I could do this with the ds-source that uses EXEC to call a script that 
collects the SNMP values for me and then does the math to create a new ds, 
but it would be a whole lot cleaner if I can do it all inside of Cricket 
and not have to mess with an external script.

Does anyone have any suggestions?

Thanks.

Clarke Morledge
College of William and Mary
Information Technology - Network Engineering
Jones Hall (Room 18)
Williamsburg VA 23187

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