9 Oct
2004
9 Oct
'04
5:02 p.m.
On Sun, 10 Oct 2004, der Mouse wrote:
The lowly 8080 had DAA, Decimal Adjust for Addition. If I recall,
it handled "carry" from bit5 (and Cy?) after adding a BCD pair
in A.
Man, I wrote a lot of 8080 code, so much I still remember
opcodes and could puzzle out binary 20 years later, but it's
possible I never once used DAA. Hell, I used MOV A, A even.
(An inline pseudo-disassembler; a config file could specify
the IO port a tape drive interface was located and the program
modified itself to change all the port numbers for IN and
OUT. IO instructions following MOV A, A were modified.)
> I've
always wondered what systems/processors (other than IBM
> mainframes) that had hardware decimal arithmetic support.
The VAX has packed decimal arithmetic instructions. Depending on which
VAX, they may be microcoded or they may just trap to the OS for
"macrocoded" emulation (of course the OS may choose to error out
instead of bothering).