Compilers and languages (Was: Help reading a 9 track tape

Chuck Guzis cclist at
Tue Aug 3 15:41:09 CDT 2021

On 8/3/21 1:12 PM, Paul Koning wrote:
>> On Aug 3, 2021, at 3:28 PM, Chuck Guzis <cclist at> wrote:
>> ...
>> One of my favorite 6000 bits of code was the register save and restore
>> routines (not using CEJ).  It was a favorite interview question for
>> those job seekers claiming to be proficient in COMPASS.
> ALL the registers, right?  I remember seeing that problem description.  And later I saw the code, don't remember it but now I know how it is done.

Yup, the trick is getting the first 18 bit register saved.  Not obvious
since normal stores are done through the (A6,X6 and A7,X7) registers.
The trick is using RJ instructions to store an indication of each bit of
a B-register.  After you get one register saved this way, the rest falls
out like a stacked deck in Solitaire.


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