RFR 8015978: Incorrect transformation of XPath expression "string(-0)"

[Joe Darcy]

Hi Aleksej,

On 6/10/2013 8:02 AM, Aleksej Efimov wrote:
> Hi Joe,
> We can replace the "Double.isNaN(d) || Double.isInfinite(d)" with 
> "!Double.isFinite(d)" - I agree that this one check looks better, but 
> we still need to do the -0.0 -> 0.0 conversion to solve the reported 
> problem. And as I understand (might be wrong) modification of this 
> check won't help us to achieve this goal, we still need to do the 
> conversion:
> +            //Convert -0.0 to +0.0 other values remains the same
> +            d = d + 0.0;
> +

Right; changing the set of Double.isFoo methods called earlier doesn't 
change the need for the (d + 0.0) expression. I just noticed the double 
isFoo calls when looking at the code and saw an opportunity to use the 
new method.

Cheers,

-Joe


> Regards,
> -Aleksej
>
> On 06/09/2013 10:23 PM, Joe Darcy wrote:
>> Hello Aleksej,
>>
>> Looking at the code, I have another suggestion. If this code can run 
>> exclusively on JDK 8 or later, replace
>>
>>  955             if (Double.isNaN(d) || Double.isInfinite(d))
>>  956                 return(Double.toString(d));
>>
>> with
>>
>>  955             if (!Double.isFinite(d))
>>  956                 return(Double.toString(d));
>>
>> Cheers,
>>
>> -Joe
>>
>> On 6/9/2013 11:18 AM, Aleksej Efimov wrote:
>>> Joe,
>>>
>>> I definitely like it:
>>> 1. Its a one-line change - perfect size.
>>> 2. Its fastest one from discussed previously.
>>> 3. -0.0 -> 0.0 has tests.
>>> 4. And it solves our problem.
>>>
>>> As a result of all props the next version of webrev: 
>>> http://cr.openjdk.java.net/~coffeys/webrev.8015978.v2/ 
>>> <http://cr.openjdk.java.net/%7Ecoffeys/webrev.8015978.v2/>
>>>
>>> Thanks
>>> -Aleksej
>>>
>>> On 06/07/2013 11:11 PM, huizhe wang wrote:
>>>> Nice. One-line change, I guess Aleksej would love it :-)
>>>>
>>>> On 6/7/2013 10:19 AM, Joe Darcy wrote:
>>>>> I'll do you one better; you can turn a negative zero into a 
>>>>> positive zero leaving other values unchanged like this:
>>>>>
>>>>>     d = d + 0.0;
>>>>>
>>>>> In IEEE 754 under the round-to-nearest-even rounding mode required 
>>>>> by Java
>>>>>     -0.0 + 0.0 => (+)0.0
>>>>>
>>>>> This trick is used in various places in Java's numerical 
>>>>> libraries, is required behavior by our specifications, and even 
>>>>> has some tests for it :-)
>>>>>
>>>>> -Joe
>>>>>
>>>>> On 6/7/2013 8:43 AM, David Chase wrote:
>>>>>> Wouldn't be more efficient to do the following, assuming that the 
>>>>>> full Java compilation chain respects the trickiness of 0 vs -0:
>>>>>>
>>>>>>     if (d == 0.0) {
>>>>>>          d=0.0 // Jam -0 == +0 to +0, per 
>>>>>> http://www.w3.org/TR/xpath/#function-string
>>>>>>
>>>>>>     }
>>>>>>
>>>>>> Division's plenty more expensive than assigning a constant, 
>>>>>> especially on platforms that lack hardware FP division.
>>>>>>
>>>>>> David
>>>>>>
>>>>>> On 2013-06-07, at 2:03 AM, huizhe wang <huizhe.wang at oracle.com> 
>>>>>> wrote:
>>>>>>
>>>>>>> Hi Aleksej,
>>>>>>>
>>>>>>> According to XPath spec, both positive and negative zero are 
>>>>>>> converted to the string 0, so it seems doesn't matter. But if 
>>>>>>> you want to detect the negative zero, you may do the following:
>>>>>>>     if (d == 0.0 && 1/d < 0.0) {
>>>>>>>          d=0.0
>>>>>>>     }
>>>>>>>
>>>>>>> Recognizing that (-0.0 == 0.0), and (1/(-0.0) == -Infinity).
>>>>>>>
>>>>>>> -Joe
>>>>>>
>>>>>
>>>>
>>>
>>
>