Rich kids are into COBOL
elson at pico-systems.com
Sun Mar 1 10:41:53 CST 2015
On 03/01/2015 05:42 AM, Johnny Billquist wrote:
> The SKIP paradigm isn't so bad, in my mind. Sometimes it's
> really handy.
Yeah, SOMETIMES. But, a conditional branch ended up always
being two instructions.
> Return address in the first word is also not so bad,
> unless you want to recurse, or have reentrant code.
> I haven't properly looked at the 18-bit machines, but I
> suspect the 13 bit address field is not much different
> from the 7 bit address field of a PDP-8 instruction.
> The ones and twos complement is the most interesting part.
> I suspect that is because they really had decided that
> twos complement was the future. However, the DEC 18-bit
> series really started with the PDP-1, and all follow on
> machines were somewhat backwards compatible, and the PDP-1
> was actually a ones complement machine. The only one DEC
> built that way. So all followon 18-bitters would have to
> keep the capability, I guess.
I did a bit of work on the LINC, which was ones complement.
The messy bit was that
if you compared negative zero against positive zero, you got
a not-equal indication.
So, you needed two compare strategies to be sure to know
that -0 really did equal +0.
UGLY! Of course, it would have cost a bunch of gates to fix
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