ifindex numbers

I am trying to decode some counter samples and I ran into the
following problem. I want to separate the information in the ifindex
fields. For Force10 devices I can follow the procedure described here
https://www.force10networks.com/csportal20/KnowledgeBase/SNMPFAQ.aspx
under "How are ifIndexes calculated? " I also have HP devices which
use non-expanded ifindexes. My question is does anyone know if this is
standardized somewhere or do I really need to implement different
decoding for each specific vendor ? And if the altter is the case, how
can you know which vendor the device belongs to from the information
in the datagram / counter samples (if this is even possible)

-- 
Rune V. Sjoen
You always pass failure on the way to success