Always false float comparisons

[Manu via Digitalmars-d]

On 10 May 2016 at 06:25, Marco Leise via Digitalmars-d
<digitalmars-d at puremagic.com> wrote:
> Am Mon, 9 May 2016 02:10:19 -0700
> schrieb Walter Bright <newshound2 at digitalmars.com>:
>
>> Don Clugston pointed out in his DConf 2016 talk that:
>>
>>      float f = 1.30;
>>      assert(f == 1.30);
>>
>> will always be false since 1.30 is not representable as a float. However,
>>
>>      float f = 1.30;
>>      assert(f == cast(float)1.30);
>>
>> will be true.
>>
>> So, should the compiler emit a warning for the former case?
>
> I'd say yes, but exclude the case where it can be statically
> verified, that the comparison can yield true, because the
> constant can be losslessly converted to the type of 'f'.
>
> By example, don't warn for these:
> f == 1.0, f == -0.5, f == 3.625, f == 2UL^^60
>
> But do warn for:
> f == 1.30, f == 2UL^^60+1
>
> As an extension of the existing "comparison is always
> false/true" check it could read "Comparison is always false:
> literal 1.30 is not representable as 'float'".
>
> There is a whole bunch in this warning category:
>   byte b;
>   if (b == 1000) {}
> "Comparison is always false: literal 1000 is not representable
> as 'byte'"
>
> --
> Marco

This.