Always false float comparisons

[Iain Buclaw via Digitalmars-d]

On 16 May 2016 at 08:00, Ola Fosheim Grøstad via Digitalmars-d
<digitalmars-d at puremagic.com> wrote:
> On Sunday, 15 May 2016 at 22:49:27 UTC, Walter Bright wrote:
>>
>> On 5/15/2016 2:06 PM, Ola Fosheim Grøstad wrote:
>>>
>>> The net result is that adding const/immutable to a type can change the
>>> semantics
>>> of the program entirely at the whim of the compiler implementor.
>>
>>
>> C++ Standard allows the same increased precision, at the whim of the
>> compiler implementor, as quoted to you earlier.
>>
>> What your particular C++ compiler does is not relevant, as its behavior is
>> not required by the Standard.
>
>
> This is a crazy attitude to take. C++ provides means to detect that IEEE
> floats are being used in the standard library. C/C++ supports non-standard
> floating point because some platforms only provide non-standard floating
> point. They don't do it because it is _desirable_ in general.
>
> You might as well say that you are not required to drive on the right side
> on the road, because you occasionally have to drive on the left. So
> therefore it is ok to always drive on left.
>
>> My proposal removes the "whim" by requiring 128 bit precision for CTFE.
>
>
> No, D's take on floating point is FUBAR.
>
> const float value = 1.30;
> float  copy = value;
> assert(value*0.5 ==  copy*0.5); // FAILS! => shutdown
>

This says more about promoting float operations to double than
anything else, and has nothing to do with CTFE.