Keep DAA! (was Re: 8086 bugs)
mouse at Rodents.Montreal.QC.CA
Sun Dec 11 01:52:47 CST 2005
>> Now, how about lowercase hex (a-f instead of A-F)? Adjusting by 39
>> instead of 7 would be a sufficient pain that I do not consider this
>> algorithm suitable.
> You don't need to, just OR the result with $20.
Grr, that's annoying. Here I was trying to come up with a way to do
conditional arithemtic in a single register without conditionals, and
you point out it's unnecessary. I was close, too - using rotates
through the carry and then instructions like SBI $00. I think it's
possible, though it needs lots of rotates. (Sequences like: use Dave
Dunfield's code up through the second-last instruction (SBI $09), then
SBI $F5; RLC; RLC; RLC; RLC; SBI $00; RRC; RRC; RRC; RRC. That gives
too wide a gap, but I think it could be modified into the kind of
solution I was thinking about.)
Still, it was fun to work on. Trying to do things in a ridiculously
constrained environment (like conditional arithmetic without
conditionals) can be fun.
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