PDP-8 signed overflow detection
Pontus Pihlgren
pontus at Update.UU.SE
Thu Mar 21 10:37:26 CDT 2019
Hmm, sounds like a fun thing to figure out. How about this for a start.
Naive, written five minutes before I have to catch my bus, untested.
I hope I understood the problem at least :)
/P
SATSUM,0
CLA CLL
TAD I SATSUM
ISZ SATSUM
TAD I SATSUM
ISZ SATSUM
SNL
JMP I SATSUM
AND (4000)
SZA
TAD (3777)
JMP I SATSUM
On Thu, Mar 21, 2019 at 12:26:37AM -0700, Kyle Owen via cctalk wrote:
> What is the shortest subroutine on a PDP-8 which will add two variables in
> RAM and return the saturated sum (that is, returning 2047 or -2048 upon
> overflow, otherwise the sum) in the accumulator?
>
> Kyle
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