Rich kids are into COBOL
cclist at sydex.com
Sun Mar 1 14:01:21 CST 2015
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
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.
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