8030942: Explicitly state floating-point summation requirements on non-finite inputs
Reviewed-by: psandoz
--- a/jdk/src/share/classes/java/util/DoubleSummaryStatistics.java Mon Jul 28 16:24:38 2014 +0100
+++ b/jdk/src/share/classes/java/util/DoubleSummaryStatistics.java Mon Jul 28 23:46:03 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.
- *
* <p> 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.
+ *
+ * <p>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:
+ *
+ * <ul>
+ *
+ * <li>If any recorded value is a NaN, then the final sum will be
+ * NaN.
+ *
+ * <li>If the recorded values contain one or more infinities, the
+ * sum will be infinite or NaN.
+ *
+ * <ul>
+ *
+ * <li>If the recorded values contain infinities of opposite sign,
+ * the sum will be NaN.
+ *
+ * <li>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.
+ *
+ * </ul>
+ *
+ * </ul>
+ *
+ * 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
+ * <em>not</em> 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.
- *
- * <p>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.
+ * <p> 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.
--- a/jdk/src/share/classes/java/util/stream/DoubleStream.java Mon Jul 28 16:24:38 2014 +0100
+++ b/jdk/src/share/classes/java/util/stream/DoubleStream.java Mon Jul 28 23:46:03 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
@@ -470,10 +470,7 @@
* code is not necessarily equivalent to the summation computation
* done by this method.
*
- * <p>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
+ * <p>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 @@
* 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.
+ *
+ * <p>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:
+ *
+ * <ul>
+ *
+ * <li>If any element is a NaN, then the final sum will be
+ * NaN.
+ *
+ * <li>If the elements contain one or more infinities, the
+ * sum will be infinite or NaN.
+ *
+ * <ul>
+ *
+ * <li>If the elements contain infinities of opposite sign,
+ * the sum will be NaN.
+ *
+ * <li>If the elements contain infinities of one sign and
+ * an intermediate sum overflows to an infinity of the opposite
+ * sign, the sum may be NaN.
+ *
+ * </ul>
+ *
+ * </ul>
+ *
+ * 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
+ * <em>not</em> guaranteed to be preserved in the final sum.
+ *
* <p>This is a <a href="package-summary.html#StreamOps">terminal
* operation</a>.
*
@@ -555,15 +590,9 @@
* 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.
- *
- * <p>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.
+ * <p>The computed average can vary numerically and have the
+ * special case behavior as computing the sum; see {@link #sum}
+ * for details.
*
* <p>The average is a special case of a <a
* href="package-summary.html#Reduction">reduction</a>.