[PATCH] 4511638: Double.toString(double) sometimes produces incorrect results

[raffaello.giulietti at gmail.com]

On 2019-03-08 14:35, Andrew Haley wrote:
> Hi,
> 
> On 3/7/19 7:16 PM, Raffaello Giulietti wrote:
> 
>> a couple of weeks ago I tried to refactor the code assuming the 
>> existence of unsignedMultiplyHigh() (either as some future intrinsic or 
>> as a Java method) and a wider representations of g with either 127 or 
>> 128 bits:
>>      g = g1 2^64 + g0
>>
>> with either
>>      2^63 <= g1 < 2^64 (128 bits)
>>
>> or
>>      2^62 <= g1 < 2^63 (127 bits)
>>
>> Unfortunately, the resulting code of rop() isn't any simpler. That's 
>> because then an intermediate sum can overflow the 64 bits of a long. As 
>> a consequence, there's need for more elaborate logic to determine
>> the carry and other slightly more complicated computations to assemble
>> the final result. All in all, the resulting code has more operations and 
>> looks longer.
> 
> Ah, I see. I agree, we still don't quite have the full set of operations
> that we need in Java, in particular a nice way of doing an add with carry.
> 

Yes.


> Thank you for the explanation.
> 

You're welcome.


>> In the meantime I got rid of the last division. There's no division at 
>> all in the whole algorithm.
> 
> Excellent. This is looking very good indeed.
>