RFR (S) CR 8006627/8007398: Improve performance of Long.toUnsignedString0, Integer.toUnsignedString0, UUID(String) and UUID.toString

[Steven Schlansker]

On Feb 13, 2013, at 2:45 PM, Mike Duigou <mike.duigou at oracle.com> wrote:

> I have updated the patch with some of Ulf's feedback and corrected one cut-and-paste error that I made.
> 
> The updated webrev is at:
> 
> http://cr.openjdk.java.net/~mduigou/JDK-8006627/2/webrev/
> 

One last ping to make sure this doesn't slip through the cracks, as I haven't seen the commit go through the public JDK8 repo…  or maybe I missed it.

Thanks again for looking at this :-)

> Mike
> 
> On Feb 12 2013, at 18:25 , Ulf Zibis wrote:
> 
>> Am 13.02.2013 02:34, schrieb Mike Duigou:
>>> Thank you for the comments Ulf.
>>> 
>>> On Feb 12 2013, at 17:24 , Ulf Zibis wrote:
>>> 
>>>> Am 13.02.2013 00:30, schrieb Mike Duigou:
>>>>> Hi Steven;
>>>>> 
>>>>> I have updated the patch for Java 8. There's somewhat less code sharing and a bit of refactoring than your last version but the performance should be about the same or a little better.
>>>>> 
>>>>> http://cr.openjdk.java.net/~mduigou/JDK-8007398/0/webrev/
>>>> Couldn't you use String(buf, true) for all to(Unsigned)String(...) methods ?
>>> Possibly. I didn't go looking too far with looking for additional improvements.
>>> 
>>>> Instead of calculating the mask each time, you could use:
>>>> 309     private static String toUnsignedString(int i, int shift, int mask) {
>>> I think that would actually be inefficient. I haven't looked at the JITed code but the mask calculation is pretty cheap relative to parameter passing.
>> 
>> I believe, JIT will inline the code, so there would be no parameter passing.
>> 
>> Additionally the calculation of char count could be faster, if you would have short cuts like:
>> numberOfLeading2Zeros(i)
>> numberOfLeading4Zeros(i)
>> numberOfLeading8Zeros(i)
>> ...
>> So the optimum would be with separate toString methods:
>> String toBase2String(int i);
>> String toBase4String(int i);
>> String toBase8String(int i);
>> ...
>> 
>> In any case I would save 2 lines:
>> 
>> 311         int mag = Integer.SIZE - Long.numberOfLeadingZeros(i);
>> 312         int charCount = Math.max(((mag + (shift - 1)) / shift), 1);
>> 313         char[] buf = new char[charCount];
>> 316         int mask = (1 << shift) - 1;
>> 
>> -Ulf
>> 
>