Casting double to ulong weirdness

[Steven Schveighoffer via Digitalmars-d]

On 8/24/15 3:15 PM, bachmeier wrote:
> On Monday, 24 August 2015 at 18:59:58 UTC, Steven Schveighoffer wrote:
>> All this gets down to: FP cannot accurately represent decimal. Should
>> this be fixed? Can it be fixed? I don't know. But I would be very
>> cautious about converting anything FP to integers without some epsilon.
>>
>> -Steve
>
> I don't see anything that needs to be fixed, because I don't think
> anything is broken - there is nothing that violates my understanding of
> floating point precision in D.
>
> cast is not round. What is broken is a program that attempts to convert
> a double to an integer type using a cast rather than the functions that
> were written to do it correctly.

What is surprising, and possibly buggy, is that none of these operations 
involve real, but the issue only happens because under the hood, real is 
used instead of double for the multiplication.

I pretty much agree with you that the code is written incorrectly. But 
it is unfortunate it differs in the way it handles this from C. I think 
this issue has been brought up before on the newsgroup, especially where 
CTFE is involved.

-Steve