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/Kahan_summation_algorithm
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.
