RFR 8005311: Add Scalable Updatable Variables, DoubleAccumulator, DoubleAdder, LongAccumulator, LongAdder (original) (raw)

Peter Levart peter.levart at gmail.com
Tue Jan 8 15:05:48 UTC 2013

On 01/08/2013 03:38 PM, Peter Levart wrote:

On 01/07/2013 08:07 PM, Joe Darcy wrote:

Hello,

I had a question about how the double accumulation logic was intended to be used. I've taken a quick look at the code and it uses straightforward "sum = sum + nextValue" code to compute the double sum. Summing doubles values with code numerical accuracy is surprisingly tricky and if the DoubleAccumulator code is meant for wide use, I'd recommend using instead some form of compensated summation: http://en.wikipedia.org/wiki/Kahansummationalgorithm Hello Joe, It's very hard to program such algorithm in Java. Guess what prints the following code: double x = 1.0E100; double a = 1d; double y = x + a; double diff = y - x; double c = a - diff; System.out.println(diff); System.out.println(c); Do you have any idea how to do that (still using local variables)? Regards, Peter

Disregard this question. I thought I saw it reversed...

Regards, Peter

Thanks, -Joe On 1/5/2013 10:10 AM, Chris Hegarty wrote: As part of JEP 155 we are proposing to add the following public classes to support Scalable Updatable Variables, DoubleAccumulator, DoubleAdder, LongAccumulator and LongAdder. These have been written by Doug Lea, with assistance from members of the former JCP JSR-166 Expert Group. Webrev and javadoc are at: http://cr.openjdk.java.net/~chegar/8005311/ver.00/ Since Doug is the author, I am taking a reviewer/sponsor role. Here are my initial comments. - There are various places in DoubleAccmulator where there are broken links to #sum ( I think it is just a cut'n'paste error ). These should be #get. - Accumulators {@link #get} may read somewhat better as {@link #get current value} ?? - Accumulators Does the 'identity' value need further explanation? Note: There is one minor change to the implementation. Currently in the jdk8 repo j.u.f.DoubleBinaryOperator defines operateAsDouble. This method has been renamed to applyAsDouble in the lambda/lambda repo. When these changes are sync'ed from lambda/lambda this can be reverted. A similar comment has been added to the code. -Chris.

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