Very strange problem with comparing floating point numbers

[Ivan Agafonov]

On Sunday, 30 September 2012 at 06:20:56 UTC, jerro wrote:
>> The second one uses fstp twice, then fld twice. I don't know, 
>> maybe
>> this could be a bug.
>
> You're right the lack of one fst/fld in the first case is a 
> bug. x87 floating point registers are 80 bit. This:
>
> fstp    dword [ebp-0CH]
>
> Converts the value in ST0 to single precision float and stores 
> it to memory (and pops ST0). When it is later loaded with fld, 
> it is not the same as before storing since some precision is 
> lost (because the D code compares floats and not reals, this is 
> the correct behavior). In the first example, this storing and 
> loading only happens for the first function call. For the 
> second call the value is returned in ST0 and stays in x87 
> registers until it is compared with fucompp so it is not 
> truncated as the result of the first function call was. That's 
> why the compared values are not equal.

Can you or anyone report this bug? I don't know how to do this.