Has Anyone Written PDP-8 .XOR. Code Using the MQ Register (Without the EAE)?

[Don North]

On 12/23/2015 7:14 PM, Christian Gauger-Cosgrove wrote:
> On 23 December 2015 at 13:44, CLASystems <clasystems at gmail.com> 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 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. I haven't
> a clue what it does.
>
> What I have entered:
> sim> ie -m 100-105
> 100:    TAD 76
> 101:    AND 77
> 102:    CLL RAL
> 103:    CIA
> 104:    TAD 76
> 105:    DCA 77
>
> Locations 076 and 077 being ARGONE and ARGTWO respectively, at the start:
> sim> ie 076-077
> 76:     1234
> 77:     4321
>
> After running the above code sample:
> sim> ie 076-077
> 76:     1234
> 77:     0574
>
> If we "flip" ARGONE and ARGTWO's values (to 4321 and 1234 respectively):
> sim> ie 076-077
> 76:     4321
> 77:     3661
>
> Neither of those is the expected 5115 of an XOR operation.
>
> Am I missing something blindingly obvious?
>
>
> Cheers,
> Christian
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