On 7/10/25 13:12, Tony Harminc wrote:
I've been using the AHI for this for many years now because by far the most
frequent reason I want to subtract 1 from a register is to use it
immediately in an EX of an MVC or TR or the like. And in this case it's
very good to have that condition code, because you can with one BM/JM
instruction following the AHI avoid the case where your MVC or whatever
runs with a length of 256 because some earlier code didn't anticipate the
original content of Rx being 0. This is a common cause of overlays, in my
experience.
...
I suspect this is hazard is much of the reason that the old
Data Management book set a minimum of 5 for the count in
an RDW (Using Data Sets now allows 4), and part of the reason
that CMS prohibits empty records.
--
gil
