<Swing Dev> [15] RFR JDK-8220811: SpinnerNumberModel floating point rounding issue

[Sergey Bylokhov]

On 2/11/20 11:52 pm, Pankaj Bansal wrote:
> Hi Sergey,
> 
> << Sometimes there are difference:
> Ok, I see it now. So, should I just close this bug as not an issue with proper comments or make changes using Math.fma for best possible results? The probability of issue happening will decrease using Math.fma(b, c, a) as compared to normal a+b*c.

According to the source code, the multiplication is needed only to change the sign of the result so c is always -1 or 1, not sure is it possible to get some rounding issues or not(need to check somehow)?

> 
> Regards,
> Pankaj
> 
> -----Original Message-----
> From: Sergey Bylokhov
> Sent: Wednesday, February 12, 2020 1:09 PM
> To: Pankaj Bansal <pankaj.b.bansal at oracle.com>; swing-dev at openjdk.java.net
> Subject: Re: <Swing Dev> [15] RFR JDK-8220811: SpinnerNumberModel floating point rounding issue
> 
>> I am not able to find any issue with this approach.
> Sometimes there are difference:
> 
> double b = 0.10000000000000011;
> 
> constructor [1]: 0.1000000000000001165734175856414367444813251495361328125
> constructor [2]: 0.10000000000000012
> 
>> <<But it is possible to create Float.valueOf(float) and pass it to this constructor, isn't it? this will work for any primitives.
>> <<[3]     public SpinnerNumberModel(Number value,
>>                                    Comparable<?> minimum,
>>                                    Comparable<?> maximum,
>>                                    Number stepSize)
>>
>> Yes, it is true. If we create "Float" objects from primitive float and pass to the constructor, things work fine. But what if the user is passing the primitive float values directly? As the double constructor is there, it is called instead of this constructor which accepts objects. This creates issue.
>> I don’t see this in spec that users should not use primitive float directly and should first create "Float" object and then create SpinnerNumberModel. So they will use primitive floats directly and run into these issues.
> 
> This is described in the top level specification of this class.
> 
>> As I suggested earlier, either we should remove constructors with primitive double or add constructor for primitive float.
> 
> The primitive variants are there because it was decided that "integers and doubles" are quite common, so they have special constructors, this is also described in the top-level spec of the class.
> 


-- 
Best regards, Sergey.