On Thu, Mar 25, 2010 at 15:19, Ulf Zibis <ulf.zi...@gmx.de> wrote:
> Am 25.03.2010 22:47, schrieb Martin Buchholz:
>>
>> Here's another minor performance tweak to
>>
>> public String(int[] codePoints, int offset, int count) {
>>
>> that optimizes for BMP.
>>
>> // Pass 1: Compute precise size of char[]
>> int n = count;
>> for (int i = offset; i< end; i++) {
>> int c = codePoints[i];
>> if (Character.isBMPCodePoint(c))
>> ;
>> else if (Character.isSupplementaryCodePoint(c))
>> n++;
>> else throw new IllegalArgumentException(Integer.toString(c));
>> }
>>
>
> Yes, this is a valuable pattern, you found out.
> I think, it could look smarter/more clear:
>
> if (Character.isBMPCodePoint(c))
> continue;
> if (Character.isSupplementaryCodePoint(c))
> n++;
> else
> throw new IllegalArgumentException(Integer.toString(c));
>
> And this would be faster, as isSupplementaryCodePoint is not optimized for
> following isBMPCodePoint:
>
> if (Character.isBMPCodePoint(c))
> continue;
> if (!Character.isValidCodePoint(c))
> throw new IllegalArgumentException(Integer.toString(c));
> n++;
Done.
> Before you go to the meeting, maybe scan the JDK for similar use cases,
Sorry, that's your job.
> before I get addicted too, and don't forget to define c as final.
I see no reason to declare c as final here.
> It's enough, that I'm addicted from:
> // fill backwards for VM performance reasons, reduces register
> pressure, faster compare against 0
> for (int i = end; n > 0; ) {
> int c = codePoints[--i];
> if (Character.isBMPCodePoint(c))
> v[--n] = (char)c;
> else
> Character.toSurrogates(c, v, n-=2);
> }
Do you have actual evidence that this is faster?
I can see a different reason why - βουστροφηδόν traversal
is more cache-friendly.
http://en.wikipedia.org/wiki/Boustrophedon
Maybe those ancient Greeks were on to something.
Martin
