Integer overflow and underflow semantics

[Alex Rønne Petersen]

On 05-05-2012 07:32, Era Scarecrow wrote:
> On Saturday, 5 May 2012 at 04:57:48 UTC, Alex Rønne Petersen wrote:
>> Hi,
>>
>> I don't think the language really makes it clear whether overflows and
>> underflows are well-defined. Do we guarantee that for any integral
>> type T, T.max + 1 == T.min and T.min - 1 == T.max?
>>
>> This is relevant in particular for GDC and LDC since they target a lot
>> of weird architectures.
>
> Any systems that implement a carry flag likely works exactly like that.
> Carry flag is set or cleared after a math operation, allowing you to
> extend the size of your integer any level you want, like in oh the 6502?
>
> Might look something like this: Been a while but you should get the idea
>
> clc ;clear carry
> loop_here:
> mov ax, [bx]
> adc [dx], ax
> inc bx
> inc dx
> dec cx
> cmp cx, 0
> jne loop_here
>
> ;if carry after this point then...
> jc overflow_warning
>

Right, but the question was whether the language guarantees what I 
described. C and C++ don't, and IMO, we should strive to fix that.

-- 
- Alex