From 764a2d8fd8ab37d44da020e063077a7a0f54af8d Mon Sep 17 00:00:00 2001 From: Joe Darcy Date: Mon, 28 Jul 2014 23:46:03 -0700 Subject: [PATCH] 8030942: Explicitly state floating-point summation requirements on non-finite inputs Reviewed-by: psandoz --- .../java/util/DoubleSummaryStatistics.java | 55 +++++++++++++----- .../java/util/stream/DoubleStream.java | 57 ++++++++++++++----- 2 files changed, 85 insertions(+), 27 deletions(-) diff --git a/jdk/src/share/classes/java/util/DoubleSummaryStatistics.java b/jdk/src/share/classes/java/util/DoubleSummaryStatistics.java index 569c35899bc..ab5f59d8a65 100644 --- a/jdk/src/share/classes/java/util/DoubleSummaryStatistics.java +++ b/jdk/src/share/classes/java/util/DoubleSummaryStatistics.java @@ -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 @@ public class DoubleSummaryStatistics implements DoubleConsumer { * 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 @@ public class DoubleSummaryStatistics implements DoubleConsumer { * 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: + * + *

+ * + * 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 @@ public class DoubleSummaryStatistics implements DoubleConsumer { * 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. diff --git a/jdk/src/share/classes/java/util/stream/DoubleStream.java b/jdk/src/share/classes/java/util/stream/DoubleStream.java index cfc12ffde28..08b4eeda304 100644 --- a/jdk/src/share/classes/java/util/stream/DoubleStream.java +++ b/jdk/src/share/classes/java/util/stream/DoubleStream.java @@ -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 @@ -470,10 +470,7 @@ public interface DoubleStream extends BaseStream { * code is not necessarily equivalent to the summation computation * done by this method. * - *

If any stream element 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 + *

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 not defined to allow for implementation @@ -485,6 +482,44 @@ public interface DoubleStream extends BaseStream { * 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 elements. + * + *

Various conditions can result in a non-finite sum being + * computed. This can occur even if the all the elements + * being summed are finite. If any element is non-finite, + * the sum will be non-finite: + * + *

+ * + * 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 elements are all + * finite. + * + * If all the elements are zero, the sign of zero is + * not guaranteed to be preserved in the final sum. + * *

This is a terminal * operation. * @@ -555,15 +590,9 @@ public interface DoubleStream extends BaseStream { * mean of elements of this stream, or an empty optional if this * stream is empty. * - * If any recorded value is a NaN or the sum is at any point a NaN - * then the average will be 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 #sum - * 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 #sum} + * for details. * *

The average is a special case of a reduction.