Integer overflow and underflow semantics?

[Walter Bright via Digitalmars-d]

On 7/23/2014 12:49 AM, Don wrote:
> On Tuesday, 22 July 2014 at 15:31:22 UTC, Ola Fosheim Grøstad wrote:
>> D claims to focus generic programming. So it should also encourage pure
>> functions that can be specified for floats, ints and other numeric types that
>> are subtypes of (true) reals in the same clean definition.
>
> I think it's a complete fantasy to think you can write generic code that will
> work for both floats and ints. The algorithms are completely different.
>
> One of the simplest examples is that given float f;  int i;
>
> (f + 1) and  (i +  1)  have totally different semantics.
>
> There are no values of i for which i + 1 == i,
> but if abs(f) > 1/real.epsilon, then f + 1 == f.
>
> Likewise there is no value of i for which i != 0 && i+1 == 1,
> but for any abs(f) < real.epsilon, f + 1 == 1.
>
>
>> If you express the expression in a clean way to get down to the actual (more
>> limited type) then the optimizer sometimes can pick an efficient sequence of
>> instructions that might be a very fast approximation if you reduce the
>> precision sufficiently in the end-result.
>
>>
>> To get there you need to differentiate between a truncating division and a
>> non-truncating division etc.
>
> Well, it's not a small number of differences. Almost every operation is
> different. Maybe all of them. I can't actually think of a single operation where
> the semantics are the same for integers and floating point.
>
> Negation comes close, but even then you have the special cases -0.0 and
> -(-int.max - 1).
>
>
>> The philosophy behind generic programming and the requirements for efficient
>> generic programming is quite different from the the machine-level hand
>> optimizing philosophy of classic C, IMO.
>
> I think that unfortunately, it's a quest that is doomed to fail. Producing
> generic code that works for both floats and ints is a fool's errand.

I quoted you on https://github.com/D-Programming-Language/phobos/pull/2366 !