Improved speed of FastMath copysign methods.

JIRA: MATH-951

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1459887 13f79535-47bb-0310-9956-ffa450edef68

pom.xml

@@ -162,6 +162,9 @@
     <contributor>
       <name>Dan Checkoway</name>
     </contributor>
+    <contributor>
+      <name>Charles Cooper</name>
+    </contributor>
     <contributor>
       <name>Paul Cowan</name>
     </contributor>

src/changes/changes.xml

@@ -55,6 +55,9 @@ This is a minor release: It combines bug fixes and new features.
   Changes to existing features were made in a backwards-compatible
   way such as to allow drop-in replacement of the v3.1[.1] JAR file.
 ">
+      <action dev="luc" type="update" issue="MATH-951" due-to="Charles Cooper">
+        Improved speed of FastMath copysign methods.
+      </action>
       <action dev="erans" type="add" issue="MATH-817" due-to="Jared Becksfort">
         Added Multivariate Normal Mixture Model Fitting by Expectation Maximization.
       </action>

src/main/java/org/apache/commons/math3/util/FastMath.java

@@ -3630,9 +3630,13 @@ public class FastMath {
      * @return the magnitude with the same sign as the {@code sign} argument
      */
     public static double copySign(double magnitude, double sign){
-        long m = Double.doubleToLongBits(magnitude);
+        // The highest order bit is going to be zero if the
-        long s = Double.doubleToLongBits(sign);
+        // highest order bit of m and s is the same and one otherwise.
-        if ((m >= 0 && s >= 0) || (m < 0 && s < 0)) { // Sign is currently OK
+        // So (m^s) will be positive if both m and s have the same sign
+        // and negative otherwise.
+        final long m = Double.doubleToLongBits(magnitude);
+        final long s = Double.doubleToLongBits(sign);
+        if ((m^s) >= 0) {
             return magnitude;
         }
         return -magnitude; // flip sign
@@ -3647,9 +3651,13 @@ public class FastMath {
      * @return the magnitude with the same sign as the {@code sign} argument
      */
     public static float copySign(float magnitude, float sign){
-        int m = Float.floatToIntBits(magnitude);
+        // The highest order bit is going to be zero if the
-        int s = Float.floatToIntBits(sign);
+        // highest order bit of m and s is the same and one otherwise.
-        if ((m >= 0 && s >= 0) || (m < 0 && s < 0)) { // Sign is currently OK
+        // So (m^s) will be positive if both m and s have the same sign
+        // and negative otherwise.
+        final int m = Float.floatToIntBits(magnitude);
+        final int s = Float.floatToIntBits(sign);
+        if ((m^s) >= 0) {
             return magnitude;
         }
         return -magnitude; // flip sign

src/test/java/org/apache/commons/math3/util/FastMathTest.java

@@ -1149,6 +1149,10 @@ public class FastMathTest {
         double delta = 0.0;
         Assert.assertEquals(1.0, FastMath.copySign(1d, 2.0), delta);
         Assert.assertEquals(1.0, FastMath.copySign(1d, 0.0), delta);
+        Assert.assertEquals(-1.0, FastMath.copySign(1d, -0.0), delta);
+        Assert.assertEquals(1.0, FastMath.copySign(1d, Double.POSITIVE_INFINITY), delta);
+        Assert.assertEquals(-1.0, FastMath.copySign(1d, Double.NEGATIVE_INFINITY), delta);
+        Assert.assertEquals(1.0, FastMath.copySign(1d, Double.NaN), delta);
         Assert.assertEquals(-1.0, FastMath.copySign(1d, -2.0), delta);
     }
 
@@ -1157,6 +1161,10 @@ public class FastMathTest {
         float delta = 0.0F;
         Assert.assertEquals(1.0F, FastMath.copySign(1d, 2.0F), delta);
         Assert.assertEquals(1.0F, FastMath.copySign(1d, 0.0F), delta);
+        Assert.assertEquals(-1.0F, FastMath.copySign(1d, -0.0F), delta);
+        Assert.assertEquals(1.0F, FastMath.copySign(1d, Float.POSITIVE_INFINITY), delta);
+        Assert.assertEquals(-1.0F, FastMath.copySign(1d, Float.NEGATIVE_INFINITY), delta);
+        Assert.assertEquals(1.0F, FastMath.copySign(1d, Float.NaN), delta);
         Assert.assertEquals(-1.0F, FastMath.copySign(1d, -2.0F), delta);
     }