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Re: Problems with float Math.min(float,float) etc
From: |
Eric Blake |
Subject: |
Re: Problems with float Math.min(float,float) etc |
Date: |
Tue, 15 Jan 2002 09:37:18 -0700 |
Peter Dickerson wrote:
>
> Math.min(float,float) seems to have incorrect behaviour for negative zero.
>
You must have a stale file. I show CVS to have this already (which
avoids a method call, and does not have the bug you mentioned):
public static float min (float a, float b)
{
// this check for NaN, from JLS 15.21.1, saves a method call
if (a != a)
return a;
// no need to check if b is NaN; < will work correctly
// recall that -0.0 == 0.0, but [+-]0.0 - [+-]0.0 behaves special
if (a == 0 && b == 0)
return -(-a - b);
return (a < b) ? a : b;
}
However, I did notice some similar problems in Double and Float, and am
checking in the following patch.
--
This signature intentionally left boring.
Eric Blake address@hidden
BYU student, free software programmer
2002-01-15 Eric Blake <address@hidden>
* java/lang/Double.java (equals, compare): Fix 0.0 vs. -0.0 math.
* java/lang/Float.java (equals, compare): Ditto.
Index: java/lang/Double.java
===================================================================
RCS file: /cvsroot/classpath/classpath/java/lang/Double.java,v
retrieving revision 1.26
diff -u -r1.26 Double.java
--- java/lang/Double.java 15 Nov 2001 02:23:35 -0000 1.26
+++ java/lang/Double.java 15 Jan 2002 16:34:04 -0000
@@ -1,5 +1,5 @@
/* Double.java -- object wrapper for double primitive
- Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
+ Copyright (C) 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
This file is part of GNU Classpath.
@@ -44,7 +44,8 @@
*
* @author Paul Fisher
* @author Andrew Haley <address@hidden>
- * @since JDK 1.0
+ * @author Eric Blake <address@hidden>
+ * @since 1.0
*/
public final class Double extends Number implements Comparable
{
@@ -163,9 +164,12 @@
if (!(obj instanceof Double))
return false;
- Double d = (Double) obj;
+ double d = ((Double) obj).value;
- return doubleToLongBits (value) == doubleToLongBits (d.doubleValue ());
+ // common case first, then check NaN and 0
+ if (value == d)
+ return (value != 0) || (1 / value == 1 / d);
+ return isNaN(value) && isNaN(d);
}
/**
@@ -336,10 +340,9 @@
return isNaN (y) ? 0 : 1;
if (isNaN (y))
return -1;
- if (x == 0.0d && y == -0.0d)
- return 1;
- if (x == -0.0d && y == 0.0d)
- return -1;
+ // recall that 0.0 == -0.0, so we convert to infinites and try again
+ if (x == 0 && y == 0)
+ return (int) (1 / x - 1 / y);
if (x == y)
return 0;
Index: java/lang/Float.java
===================================================================
RCS file: /cvsroot/classpath/classpath/java/lang/Float.java,v
retrieving revision 1.21
diff -u -r1.21 Float.java
--- java/lang/Float.java 11 Nov 2001 16:07:09 -0000 1.21
+++ java/lang/Float.java 15 Jan 2002 16:34:04 -0000
@@ -1,5 +1,5 @@
/* java.lang.Float
- Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
+ Copyright (C) 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
This file is part of GNU Classpath.
@@ -44,7 +44,8 @@
*
* @author Paul Fisher
* @author Andrew Haley <address@hidden>
- * @since JDK 1.0
+ * @author Eric Blake <address@hidden>
+ * @since 1.0
*/
public final class Float extends Number implements Comparable
{
@@ -232,9 +233,12 @@
if (!(obj instanceof Float))
return false;
- Float f = (Float) obj;
+ float f = ((Float) obj).value;
- return floatToIntBits (value) == floatToIntBits (f.floatValue ());
+ // common case first, then check NaN and 0
+ if (value == f)
+ return (value != 0) || (1 / value == 1 / f);
+ return isNaN(value) && isNaN(f);
}
/**
@@ -484,10 +488,9 @@
return isNaN (y) ? 0 : 1;
if (isNaN (y))
return -1;
- if (x == 0.0 && y == -0.0)
- return 1;
- if (x == -0.0 && y == 0.0)
- return -1;
+ // recall that 0.0 == -0.0, so we convert to infinities and try again
+ if (x == 0 && y == 0)
+ return (int) (1 / x - 1 / y);
if (x == y)
return 0;