One more factoid:
Many who have DECtape drives do not run them at the final spec of relevant
ECOs. The TD8E will work quite as well as it can on the hardware side, but
only if you perform all lf the ECOs [or equivalent]. Some are volunteering
their time to help document [and in some instances im
On Wed, Dec 23, 2015 at 10:14 PM, Christian Gauger-Cosgrove <
captainkirk...@gmail.com> wrote:
> On 23 December 2015 at 13:44, CLASystems wrote:
> > Ironically, the shortest and fastest seems to be avoidance of the MQ
> > altogether [thus making it work on ANY model].
> >
> > TAD ARGONE
> >
Steve Gibson talks about XOR on the PDP-8 here:
https://www.grc.com/pdp-8/isp-musings.htm
In summary, Steve uses this condensed code using "carryless addition" for
XOR:
CLA/ clear accumulator (AC) since all we have is add!
TAD ArgOne / add (TAD) ArgOne to the just-zeroed AC
AND
Here's the best I've got, Bob:
ARG1, 5252
ARG2, 2525
XOR, CLA
TAD ARG1 /~ARG1 & ARG2
CMA
AND ARG2
MQL /STORE IN MQ
TAD ARG2 /ARG1 & ~ARG2
CMA
AND ARG1
MQA /MQ OR AC -> AC
/RESULT IS IN AC
You can also add them and subtract two times the arguments ANDed together,
but I haven't played with tha
as a
condition of a skip or execute.
From: cctalk on behalf of Don North
Sent: Wednesday, December 23, 2015 11:21 PM
To: cctalk@classiccmp.org
Subject: Re: Has Anyone Written PDP-8 .XOR. Code Using the MQ Register (Without
the EAE)?
On 12/23/2015 10:
On 12/23/2015 10:50 PM, Don North wrote:
On 12/23/2015 7:14 PM, Christian Gauger-Cosgrove wrote:
On 23 December 2015 at 13:44, CLASystems wrote:
Ironically, the shortest and fastest seems to be avoidance of the MQ
altogether [thus making it work on ANY model].
TAD ARGONE
AND ARGTW
: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Has Anyone Written PDP-8 .XOR. Code Using the MQ Register (Without
the EAE)?
Ok, I think I get it
The acc is one value. Both arg1 and agr0 are init to the second value ( start
the same )
I'm not sure how to save a value to the a
Topic Posts
Subject: Re: Has Anyone Written PDP-8 .XOR. Code Using the MQ Register (Without
the EAE)?
I'm not sure how to code it on the machine but I know
how to do it.
Take A AND B = C
2* C = D ( ignore carry )
negate D ( complement and add 1 )
A + B = E ( this could have been done first )
On 12/23/2015 7:14 PM, Christian Gauger-Cosgrove wrote:
On 23 December 2015 at 13:44, CLASystems wrote:
Ironically, the shortest and fastest seems to be avoidance of the MQ
altogether [thus making it work on ANY model].
TAD ARGONE
AND ARGTWO
CLL RAL
CIA
TAD ARGONE
d Off-Topic Posts
Subject: Re: Has Anyone Written PDP-8 .XOR. Code Using the MQ Register (Without
the EAE)?
On 23 December 2015 at 13:44, CLASystems wrote:
> Ironically, the shortest and fastest seems to be avoidance of the MQ
> altogether [thus making it work on ANY model].
>
>
On 23 December 2015 at 13:44, CLASystems wrote:
> Ironically, the shortest and fastest seems to be avoidance of the MQ
> altogether [thus making it work on ANY model].
>
> TAD ARGONE
> AND ARGTWO
> CLL RAL
> CIA
> TAD ARGONE
> DCA ARGTWO
>
> This works because .XOR. is a
The following is yet another way to do it [the same identities of course
apply]:
TADARGONE
ANDARGTWO
CMA
DCATEMP
TADARGONE
MQL
TADARGTWO
MQA
ANDTEMP
This method has the advantage that it also works on the straight-8 EAE
avoiding the sing
The MQ is standard on the PDP-8/E and up through the VT78 and the DECmates.
Not possible on the 8/L, but an easy option for the PDP-8/I and the PDP-12.
This could be a problem on the straight-8 [or LINC-8] with EAE though.
It's the only model where the SWP [MQA and MQL in the same instruction]
do
Has anyone written PDP-8 code for .XOR. that uses the MQ Register (when the
EAE isn't available)? If so, can you share the source code and/or the
algorithm?
Thanks,
Bob
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