[M0] request for feature

[kjstol]

hi,

the problem is, there needs to be a *directional* comparison. just
checking whether somethign is equal or not doesn't help to implement
the > operator for instance. You can do tricks with subtracting
numbers from itself, but you need to check which side you are of 0...

Same for neg: x = -x.
There's no way to do this without at least a gt or lt op, unless
there's a neg op.

(try it out :-)

Not sure what tristate means btw...

I had a quick look around in other vms and jit engines and it seems
that lt and gt are always present as basic ops. I don't see a problem
adding one of them (or > and < both) as they're very straightforward
and will likely JIT-compile to a single CPU instruction.

cheers
kjs

On Fri, May 25, 2012 at 12:19 PM, Vasily Chekalkin <bacek at bacek.com> wrote:
> Hello.
>
> What about tristate cmp and trilabel jmpif? :)
>
> (Half jocking there)
>
> Bacek
>
> On May 25, 2012 8:55 PM, "kjstol" <parrotcode at gmail.com> wrote:
>>
>> hi there,
>>
>> I'm making nice progress on M1, the C-like language that compiles to M0.
>> However, I'm missing an essential op in M0, which is a comparison op
>> like < or >. At least one of them is necessary in order to implement
>> the <, >, <=, >= operators. the unary minus (-x) also could use it,
>> but adding a "neg" opcode would be sufficient for that of course.
>>
>> So, the request is to add at least 1 op to M0, namely either ">" or
>> "<". (gt, lt). Both is preferable, but if it's essential to keep the
>> number of ops to a minimum, then 1 is fine. (One could argue that we
>> could get rid of "mul_i" as that can be implemented by repeatedly
>> adding... :-)
>>
>> best regards,
>> kjs
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