On 25 March 2013 10:46, <[email protected]> wrote:
> Author: luc
> Date: Mon Mar 25 10:46:42 2013
> New Revision: 1460604
>
> URL: http://svn.apache.org/r1460604
> Log:
> Improved speed of FastMath.abs methods, by removing branching.
>
> JIRA: MATH-954
>
> Modified:
> commons/proper/math/trunk/src/changes/changes.xml
>
> commons/proper/math/trunk/src/main/java/org/apache/commons/math3/util/FastMath.java
>
> Modified: commons/proper/math/trunk/src/changes/changes.xml
> URL:
> http://svn.apache.org/viewvc/commons/proper/math/trunk/src/changes/changes.xml?rev=1460604&r1=1460603&r2=1460604&view=diff
> ==============================================================================
> --- commons/proper/math/trunk/src/changes/changes.xml (original)
> +++ commons/proper/math/trunk/src/changes/changes.xml Mon Mar 25 10:46:42 2013
> @@ -55,10 +55,13 @@ This is a minor release: It combines bug
> 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-954" due-to="Charles
> Cooper">
> + Improved speed of FastMath.abs methods for all signatures, by
> removing branching.
> + </action>
> <action dev="luc" type="update" issue="MATH-953" due-to="Charles
> Cooper">
> Improved speed of several FastMath methods.
> </action>
> - <action dev="luc" type="fix" issue="MATH-934">
> + <action dev="luc" type="fix" issue="MATH-934">
> Fixed Complex.reciprocal() for zero argument.
> </action>
> <action dev="luc" type="update" issue="MATH-951" due-to="Charles
> Cooper">
>
> Modified:
> commons/proper/math/trunk/src/main/java/org/apache/commons/math3/util/FastMath.java
> URL:
> http://svn.apache.org/viewvc/commons/proper/math/trunk/src/main/java/org/apache/commons/math3/util/FastMath.java?rev=1460604&r1=1460603&r2=1460604&view=diff
> ==============================================================================
> ---
> commons/proper/math/trunk/src/main/java/org/apache/commons/math3/util/FastMath.java
> (original)
> +++
> commons/proper/math/trunk/src/main/java/org/apache/commons/math3/util/FastMath.java
> Mon Mar 25 10:46:42 2013
> @@ -2987,7 +2987,8 @@ public class FastMath {
> * @return abs(x)
> */
> public static int abs(final int x) {
> - return (x < 0) ? -x : x;
> + final int i = x >>> 31;
> + return (x ^ (~i + 1)) + i;
Are we sure that's faster?
Surely branches aren't significantly slower than arithmetic operations.
> }
>
> /**
> @@ -2996,7 +2997,12 @@ public class FastMath {
> * @return abs(x)
> */
> public static long abs(final long x) {
> - return (x < 0l) ? -x : x;
> + final long l = x >>> 63;
> + // l is one if x negative zero else
> + // ~l+1 is zero if x is positive, -1 if x is negative
> + // x^(~l+1) is x is x is positive, ~x if x is negative
> + // add around
> + return (x ^ (~l + 1)) + l;
> }
>
> /**
> @@ -3005,7 +3011,10 @@ public class FastMath {
> * @return abs(x)
> */
> public static float abs(final float x) {
> - return (x < 0.0f) ? -x : (x == 0.0f) ? 0.0f : x; // -0.0 => +0.0
> + if ((Float.floatToRawIntBits(x) & Integer.MIN_VALUE) == 0) {
> + return x;
> + }
> + return -x;
> }
>
> /**
> @@ -3014,7 +3023,10 @@ public class FastMath {
> * @return abs(x)
> */
> public static double abs(double x) {
> - return (x < 0.0) ? -x : (x == 0.0) ? 0.0 : x; // -0.0 => +0.0
> + if ((Double.doubleToRawLongBits(x) & Long.MIN_VALUE) == 0) {
> + return x;
> + }
> + return -x;
> }
>
> /**
>
>
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