[commons-statistics] 02/07: Pre-compute constant

[aherbert]

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aherbert pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/commons-statistics.git

commit 1c7fe24218bd6e778e894d02086142e2bd114c9c
Author: Alex Herbert <aherb...@apache.org>
AuthorDate: Thu Oct 21 13:23:51 2021 +0100

    Pre-compute constant
---
 .../apache/commons/statistics/distribution/NormalDistribution.java    | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git 
a/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/NormalDistribution.java
 
b/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/NormalDistribution.java
index a7d7141..fdca0b0 100644
--- 
a/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/NormalDistribution.java
+++ 
b/commons-statistics-distribution/src/main/java/org/apache/commons/statistics/distribution/NormalDistribution.java
@@ -30,6 +30,8 @@ import 
org.apache.commons.rng.sampling.distribution.ZigguratSampler;
 public final class NormalDistribution extends AbstractContinuousDistribution {
     /** &radic;(2). */
     private static final double SQRT2 = Math.sqrt(2.0);
+    /** 0.5 * ln(2 * pi). Computed to 25-digits precision. */
+    private static final double HALF_LOG_2_PI = 0.9189385332046727417803297;
     /** Mean of this distribution. */
     private final double mean;
     /** Standard deviation of this distribution. */
@@ -47,7 +49,7 @@ public final class NormalDistribution extends 
AbstractContinuousDistribution {
                                double sd) {
         this.mean = mean;
         standardDeviation = sd;
-        logStandardDeviationPlusHalfLog2Pi = Math.log(sd) + 0.5 * Math.log(2 * 
Math.PI);
+        logStandardDeviationPlusHalfLog2Pi = Math.log(sd) + HALF_LOG_2_PI;
         sdSqrt2 = sd * SQRT2;
     }