1 Mar
2015
1 Mar
'15
11:43 p.m.
On 03/01/2015 03:05 PM, Toby Thain wrote:
Studying the CDC 6000 instruction set (through the
Grishman book) really
gives me the impression one's complement would be quite a headache to
use correctly.
It wasn't, trust me. Because the long add unit on the 6600 used a
subtractive algoritm, negative zero was pretty uncommon as a result of
arithmetic operations.
Either value registered as zero for the conditionals--remember, no
condition codes. The big difference is that negative zero registered as
minus. Remember that on X-register tests, you could, with a single
instruction, only branch on zero/nonzero or minus/plus.
--Chuck