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

Mike Duigou mike.duigou at oracle.com
Wed Mar 20 22:47:32 UTC 2013

Hi Steven;

I haven't forgotten and it's still in my queue for Java 8. I haven't had time to respond to Martin Buchholz's feedback.

http://mail.openjdk.java.net/pipermail/core-libs-dev/2013-February/014528.html

I suspect he is right about computing digits vs the table being a better choice but I would want to test that first with a proper microbenchmark (and then fix a bunch of other places that use the same table).

If you have time to follow up on any of this things will go quicker. :-)

Mike

On Mar 20 2013, at 15:39 , Steven Schlansker wrote:

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

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