Joined: 06 Jun 2008 Posts: 8218 Location: Dubuque, Iowa, USA
Find the Principles of Operation manual on the IBM web ste. It lists the translation of every assembler instruction, including this one on page 8.6:
AP D1(L1,B1),D2(L2,B2) is the instruction where
FA means Add Decimal (IBM's term for Add Packed)
4 length of D1 (lengths in translation are 1 less, so the 5 becomes a 4)
1 length of D2
D base register B1 (13 is D)
1D8 offset D1 (472 is 1D8 hex)
D base register B2 (13 is D)
1D0 offset D2 (464 is 1D0 hex)
You have to ensure that all the compile options which affect code are the same when you did the recompile.
A short-cut to that probably being true is if the dump is pointing to the identical instruction.
000D8E FA41 D1D8 D1D0 AP 472(5,13),464(2,13)
There is more than that on the listing, further to the right. That is useful stuff, so please post it, even if you have to split the line.
The instruction is decimal addition. If you conver D, 1D8 and 1D0 to decimal, you'll see the relationship to the second part shown (after the AP). The 4 and 1 are also telling you something, which appears in the second part as 5 and 2.
Check out the Principles of Operation for a full understanding of the instruction, let us know if there is something there you don't understand.