Rich kids are into COBOL

[Chuck Guzis]

On 03/01/2015 11:36 AM, Johnny Billquist wrote:

> You won't get an argument from me about that. Ones complement really is
> not something I like. And obviously DEC wasn't going for it either,
> witnessed by the fact that no machine after the PDP-1 used it. (Unless
> you count the backwards compatible stuff to the PDP-1).

I don't know--I'm of mixed feelings about it. I've been on both sides.

If -0 and +0 both tested as zero, that was fine in most cases.  Worst 
case, you added +0 to the value in question, which would have the effect 
of converting -0 to +0.

Ones complement has the curious benefit that some bit-twiddling 
operations can be very useful and not possible otherwise in two's 
complement.

See: http://www.fourmilab.ch/documents/univac/cute_tricks.html for 
similar tracks on the Univac 1100 series.

What I've developed a definite distaste for is condition codes on 
machines with significant register files.  I can understand their 
application in memory-to-memory architectures, but on register or 
register-memory, they make little sense and get in the way, particularly 
when scheduling instructions.  For me, that's one of the biggest 
drawbacks of the x86 architecture.

--Chuck