On 8/2/25 15:38, Rupert Reynolds wrote:
The classic dirty trick I saw was a branch 'ladder' where R15 had a return
code (must be in multiples of 4!) and the first branch would jump to one of
several following branches to real code.
...
In the Classic era that was not considered dirty.
I believe it was the motive for making return
codes multiples of 4. Anything else, such aw:
L Rx,TABLE(R15)
BR Rx
might require another register, two bytes for BR,
and TABLE would need fullword alignment.
Woe betide if R15 held 3, -1 etc :-)
...
If you're conscientious you should validate R15
before an indexed branch. If you're truly phobic
you should reestablish code base before storage
reference.
--
gil
