Re: Binary bit map in IBM i (was as/400)

On Wed, 19 Apr 2023 at 11:43, Jon Paris <jon.paris@xxxxxxxxxxxxxx> wrote:

You can't map binary values to EBCDIC; it wouldn't help if you could.

You just need to use RPG's bitwise operations %BITxxx against the bitmap field.

This is probably the right answer for the RPG list.

However - looking at the definition of ISO8583 bitmaps here: https://en.wikipedia.org/wiki/ISO_8583 <https://en.wikipedia.org/wiki/ISO_8583> it might be simpler to convert the whole bitmap string to an array by repetitively dividing by zero. A value of 1 indicating that the field in question is present.

It really depends on what you want to do. For example, using the %BITxxx BIFs would be the most useful if you just want to know "does the message include field x" and the division approach is better if you need to know which fields need to be processed.

OP probably needs to decode an ISO-8583 message from a payment card transaction.

Yes, the bitmap is sort of like a null map - if bit 4 (leftmost bit =
bit 1) is on, the transaction amount field is present.
For RPG purposes, note that the bitmap is a minimum of eight bytes =
64 bits, but can be longer than that depending on bit 1 of the
mandatory primary bitmap. This means that %BIT needs to be wrapped in
a loop that substrings out one byte at a time, and include the
provision to continue to secondary and tertiary bitmaps if necessary.

Reading the bits is only one step in unraveling the entire message.

It is also possible that there is an underlying MI instruction that may be surfaced that will perfomr the equivalent iof the array operation but I'm not familiar with it.

And then of course you could always call PHP, Python, node from RPG to perform the operation.

Yes, exactly. There are several Python and Java libraries that handle
one or more of the various flavours of ISO-8583.

Since each vendor has their own implementation of 8583, probably the
best advice I can give OP for the meta problem of 'How do I decode an
ISO-8583 message?' is to ask the vendor for recommendations. In
particular, ask the vendor for documentation and some sample messages
you can work with, both serialised/encoded and deserialised/decoded in
order to prove that your RPG code works as expected. If someone were
to force me to use SQL, I would probably write a UDTF that would take
the message as input and emit a result set of the various fields in
the message. Thankfully, we can write UDTF's in RPG and register them
with Db2 so that other clients can access the functionality (for
example ODBC). With a UDTF, you could do something like select
transaction_amount from table(decode_8583(select iso_data from
isofile)) iso;

--buck