JDK 9 RFR of JDK-8030942: Explicitly state floating-point summation requirements on non-finite inputs (original) (raw)

Paul Sandoz paul.sandoz at oracle.com
Mon Jul 28 14:11:33 UTC 2014

In response to previous feedback, I propose this revised change to the specification:

+1

Paul.

--- a/src/share/classes/java/util/DoubleSummaryStatistics.java Sat Jul 19 11:22:08 2014 +0800 +++ b/src/share/classes/java/util/DoubleSummaryStatistics.java Mon Jul 21 18:02:54 2014 -0700 @@ -1,5 +1,5 @@ /* - * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved. + * Copyright (c) 2012, 2014, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it @@ -129,9 +129,6 @@ * Returns the sum of values recorded, or zero if no values have been * recorded. * - * If any recorded value is a NaN or the sum is at any point a NaN - * then the sum will be NaN. - * *

The value of a floating-point sum is a function both of the

* input values as well as the order of addition operations. The * order of addition operations of this method is intentionally @@ -143,6 +140,44 @@ * numerical sum compared to a simple summation of {@code double} * values. * + * Because of the unspecified order of operations and the + * possibility of using differing summation schemes, the output of + * this method may vary on the same input values. + * + *

Various conditions can result in a non-finite sum being

 + * computed. This can occur even if the all the recorded values + * being summed are finite. If any recorded value is non-finite, + * the sum will be non-finite: + * + *
    + * + *
  • If any recorded value is a NaN, then the final sum will be
    •  + * NaN. + * + *
  • If the recorded values contain one or more infinities, the
    •  + * sum will be infinite or NaN. + * + *
      + * + *
    • If the recorded values contain infinities of opposite sign,
      •  + * the sum will be NaN. + * + *
    • If the recorded values contain infinities of one sign and
      •  + * an intermediate sum overflows to an infinity of the opposite + * sign, the sum may be NaN. + * + * + * + * + * + * It is possible for intermediate sums of finite values to + * overflow into opposite-signed infinities; if that occurs, the + * final sum will be NaN even if the recorded values are all + * finite. + * + * If all the recorded values are zero, the sign of zero is + * not guaranteed to be preserved in the final sum. + * * @apiNote Values sorted by increasing absolute magnitude tend to yield * more accurate results. * @@ -193,15 +228,9 @@ * Returns the arithmetic mean of values recorded, or zero if no * values have been recorded. * - * If any recorded value is a NaN or the sum is at any point a NaN - * then the average will be code NaN. - * - *

      The average returned can vary depending upon the order in

       - * which values are recorded. - * - * This method may be implemented using compensated summation or - * other technique to reduce the error bound in the {@link #getSum - * numerical sum} used to compute the average. + *

      The computed average can vary numerically and have the

       + * special case behavior as computing the sum; see {@link #getSum} + * for details. * * @apiNote Values sorted by increasing absolute magnitude tend to yield * more accurate results.

      (With analogous changes in java/util/stream/DoubleStream.java.) Thanks, -Joe

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