23 Dec
2015
23 Dec
'15
11:55 p.m.
Without the TMP on the Nicolet
MEMA ARGONE
ANDA ARGTWO
LASH 1
ANGA
A+MA ARGONE
A+MA ARGTWO ( or A+MM ARGTWO to save in ARGTWO )
The link bit isn't used by LASH or adds on the Nicolet. It is only the carry out of an
add.
It is a little more clumsy to use as a carry. It can only be used as a condition of a skip
or execute.
________________________________________
From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Don North <north at
alum.mit.edu>
Sent: Wednesday, December 23, 2015 11:21 PM
To: cctalk at classiccmp.org
Subject: Re: Has Anyone Written PDP-8 .XOR. Code Using the MQ Register (Without the EAE)?
On 12/23/2015 10:50 PM, Don North wrote:
On 12/23/2015 7:14 PM, Christian Gauger-Cosgrove
wrote:
FYI here is a link to find the document:
http://manx.classiccmp.org/details.php/1,3191
I can't find it under dec/pdp8 on bitsavers, maybe I'm just not seeing it.
Don
On 23 December 2015 at 13:44, CLASystems
<clasystems at gmail.com> wrote:
I think
there was just a bit of brain fade in the original listing. From
DEC-08-FFAA-D PDP-8 Math Library circa 1968
the XOR routine is as follows, transcribed to SIMH:
sim> de 76 1234
sim> de 77 4321
sim> ie -m 100-107
100: CLA CLL
101: TAD 76
102: AND 77
103: CIA
104: CLL RAL
105: TAD 76
106: TAD 77
107: HLT
sim> go 100
HALT instruction, PC: 00110 (AND 0)
sim> ex ac
AC: 5115
Which produces the correct result in the AC. Locations 103/104 were swapped in
order, and location 106 was left out.
And for completeness location 100 was added to initially clear the AC/Link.
Don
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 addition ignoring the carry bits. So, knowing
they will happen, just allow them at first, then remove them.
Hmm, I just tried that in SIMH, and that doesn't XOR at all.