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6430675: Math.round has surprising behavior for 0x1.fffffffffffffp-2

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Reviewed-by: alanb
This commit is contained in:
Joe Darcy 2011-04-14 21:27:10 -07:00
parent f4ec972481
commit b4d4e3bed4
3 changed files with 121 additions and 28 deletions
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31
jdk/src/share/classes/java/lang/Math.java
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@ -1,5 +1,5 @@
/*
* Copyright (c) 1994, 2010, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 1994, 2011, 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
@ -627,11 +627,9 @@ public final class Math {
}
/**
* Returns the closest {@code int} to the argument. The
* result is rounded to an integer by adding 1/2, taking the
* floor of the result, and casting the result to type {@code int}.
* In other words, the result is equal to the value of the expression:
* <p>{@code (int)Math.floor(a + 0.5f)}
* Returns the closest {@code int} to the argument, with ties
* rounding up.
*
* <p>
* Special cases:
* <ul><li>If the argument is NaN, the result is 0.
@ -649,17 +647,17 @@ public final class Math {
* @see java.lang.Integer#MIN_VALUE
*/
public static int round(float a) {
return (int)floor(a + 0.5f);
if (a != 0x1.fffffep-2f) // greatest float value less than 0.5
return (int)floor(a + 0.5f);
else
return 0;
}
/**
* Returns the closest {@code long} to the argument. The result
* is rounded to an integer by adding 1/2, taking the floor of the
* result, and casting the result to type {@code long}. In other
* words, the result is equal to the value of the expression:
* <p>{@code (long)Math.floor(a + 0.5d)}
* <p>
* Special cases:
* Returns the closest {@code long} to the argument, with ties
* rounding up.
*
* <p>Special cases:
* <ul><li>If the argument is NaN, the result is 0.
* <li>If the argument is negative infinity or any value less than or
* equal to the value of {@code Long.MIN_VALUE}, the result is
@ -676,7 +674,10 @@ public final class Math {
* @see java.lang.Long#MIN_VALUE
*/
public static long round(double a) {
return (long)floor(a + 0.5d);
if (a != 0x1.fffffffffffffp-2) // greatest double value less than 0.5
return (long)floor(a + 0.5d);
else
return 0;
}
private static Random randomNumberGenerator;

20
jdk/src/share/classes/java/lang/StrictMath.java
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@ -1,5 +1,5 @@
/*
* Copyright (c) 1999, 2010, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 1999, 2011, 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
@ -613,11 +613,8 @@ public final class StrictMath {
public static native double pow(double a, double b);
/**
* Returns the closest {@code int} to the argument. The
* result is rounded to an integer by adding 1/2, taking the
* floor of the result, and casting the result to type {@code int}.
* In other words, the result is equal to the value of the expression:
* <p>{@code (int)Math.floor(a + 0.5f)}
* Returns the closest {@code int} to the argument, with ties
* rounding up.
*
* <p>Special cases:
* <ul><li>If the argument is NaN, the result is 0.
@ -635,15 +632,12 @@ public final class StrictMath {
* @see java.lang.Integer#MIN_VALUE
*/
public static int round(float a) {
return (int)floor(a + 0.5f);
return Math.round(a);
}
/**
* Returns the closest {@code long} to the argument. The result
* is rounded to an integer by adding 1/2, taking the floor of the
* result, and casting the result to type {@code long}. In other
* words, the result is equal to the value of the expression:
* <p>{@code (long)Math.floor(a + 0.5d)}
* Returns the closest {@code long} to the argument, with ties
* rounding up.
*
* <p>Special cases:
* <ul><li>If the argument is NaN, the result is 0.
@ -662,7 +656,7 @@ public final class StrictMath {
* @see java.lang.Long#MIN_VALUE
*/
public static long round(double a) {
return (long)floor(a + 0.5d);
return Math.round(a);
}
private static Random randomNumberGenerator;

98
jdk/test/java/lang/Math/RoundTests.java Normal file
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@ -0,0 +1,98 @@
/*
* Copyright (c) 2011, 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
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
/*
* @test
* @bug 6430675
* @summary Check for correct implementation of {Math, StrictMath}.round
*/
public class RoundTests {
public static void main(String... args) {
int failures = 0;
failures += testNearFloatHalfCases();
failures += testNearDoubleHalfCases();
if (failures > 0) {
System.err.println("Testing {Math, StrictMath}.round incurred "
+ failures + " failures.");
throw new RuntimeException();
}
}
private static int testNearDoubleHalfCases() {
int failures = 0;
double [][] testCases = {
{+0x1.fffffffffffffp-2, 0.0},
{+0x1.0p-1, 1.0}, // +0.5
{+0x1.0000000000001p-1, 1.0},
{-0x1.fffffffffffffp-2, 0.0},
{-0x1.0p-1, 0.0}, // -0.5
{-0x1.0000000000001p-1, -1.0},
};
for(double[] testCase : testCases) {
failures += testNearHalfCases(testCase[0], (long)testCase[1]);
}
return failures;
}
private static int testNearHalfCases(double input, double expected) {
int failures = 0;
failures += Tests.test("Math.round", input, Math.round(input), expected);
failures += Tests.test("StrictMath.round", input, StrictMath.round(input), expected);
return failures;
}
private static int testNearFloatHalfCases() {
int failures = 0;
float [][] testCases = {
{+0x1.fffffep-2f, 0.0f},
{+0x1.0p-1f, 1.0f}, // +0.5
{+0x1.000002p-1f, 1.0f},
{-0x1.fffffep-2f, 0.0f},
{-0x1.0p-1f, 0.0f}, // -0.5
{-0x1.000002p-1f, -1.0f},
};
for(float[] testCase : testCases) {
failures += testNearHalfCases(testCase[0], (int)testCase[1]);
}
return failures;
}
private static int testNearHalfCases(float input, float expected) {
int failures = 0;
failures += Tests.test("Math.round", input, Math.round(input), expected);
failures += Tests.test("StrictMath.round", input, StrictMath.round(input), expected);
return failures;
}
}