Reproduction micros

Chuck Guzis cclist at
Mon Jul 25 11:19:58 CDT 2016

On 07/25/2016 02:31 AM, Peter Corlett wrote:

> Eliminating condition codes just moves the complexity from the ALU to
> the branch logic (which now needs its own mini-ALU for comparisons),
> and there's not much in it either way. Where it *does* win is that
> the useful instructions are all single-output and so one can use the
> noddy code generators found in undergraduate-level compiler
> construction textbooks such as the Dragon Book.

Sorry, I'm not following this bit.  I am speaking about a three-address
ISA here, BTW.

Simply adding a flag to each register reflecting its zero/nonzero
content should do the job.  The high-order (sign) bit is the only other
bit necessary.  Branch instructions need only inquire if either, neither
or both flags are set.

I suppose that one could also have several flags registers, being set
selectively as dictated by a field in the instruction.


More information about the cctalk mailing list