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commit 085ee67661a1e98ff3cb114ab7c4ab47e0c6a05a
Author: Alex Herbert <aherb...@apache.org>
AuthorDate: Mon Jul 5 17:52:22 2021 +0100
Faster method for a signed double in [-1, 1)
---
.../sampling/shape/UnitBallSamplerBenchmark.java | 27 +++++++++++++++++++++-
.../rng/sampling/shape/UnitBallSampler.java | 18 ++++++++++-----
2 files changed, 38 insertions(+), 7 deletions(-)
diff --git
a/commons-rng-examples/examples-jmh/src/main/java/org/apache/commons/rng/examples/jmh/sampling/shape/UnitBallSamplerBenchmark.java
b/commons-rng-examples/examples-jmh/src/main/java/org/apache/commons/rng/examples/jmh/sampling/shape/UnitBallSamplerBenchmark.java
index 87b911b..142d75d 100644
---
a/commons-rng-examples/examples-jmh/src/main/java/org/apache/commons/rng/examples/jmh/sampling/shape/UnitBallSamplerBenchmark.java
+++
b/commons-rng-examples/examples-jmh/src/main/java/org/apache/commons/rng/examples/jmh/sampling/shape/UnitBallSamplerBenchmark.java
@@ -151,13 +151,15 @@ public class UnitBallSamplerBenchmark {
public static class Sampler1D extends SamplerData {
/** Name for the signed double method. */
private static final String SIGNED_DOUBLE = "signedDouble";
+ /** Name for the signed double method, version 2. */
+ private static final String SIGNED_DOUBLE2 = "signedDouble2";
/** Name for the two doubles method. */
private static final String TWO_DOUBLES = "twoDoubles";
/** Name for the boolean double method. */
private static final String BOOLEAN_DOUBLE = "booleanDouble";
/** The sampler type. */
- @Param({BASELINE, SIGNED_DOUBLE, TWO_DOUBLES, BOOLEAN_DOUBLE})
+ @Param({BASELINE, SIGNED_DOUBLE, SIGNED_DOUBLE2, TWO_DOUBLES,
BOOLEAN_DOUBLE})
private String type;
/** {@inheritDoc} */
@@ -178,6 +180,14 @@ public class UnitBallSamplerBenchmark {
return new double[] {makeSignedDouble(rng.nextLong())};
}
};
+ } else if (SIGNED_DOUBLE2.equals(type)) {
+ return new Sampler() {
+ @Override
+ public double[] sample() {
+ // Sample [-1, 1) uniformly
+ return new double[]
{makeSignedDouble2(rng.nextLong())};
+ }
+ };
} else if (TWO_DOUBLES.equals(type)) {
return new Sampler() {
@Override
@@ -739,6 +749,21 @@ public class UnitBallSamplerBenchmark {
* @return the double
*/
private static double makeSignedDouble(long bits) {
+ // As per o.a.c.rng.core.utils.NumberFactory.makeDouble(long) but
using a signed
+ // shift of 10 in place of an unsigned shift of 11.
+ return (bits >> 10) * 0x1.0p-53d;
+ }
+
+ /**
+ * Creates a signed double in the range {@code [-1, 1)}. The magnitude is
sampled evenly
+ * from the 2<sup>54</sup> dyadic rationals in the range.
+ *
+ * <p>Note: This method will not return samples for both -0.0 and 0.0.
+ *
+ * @param bits the bits
+ * @return the double
+ */
+ private static double makeSignedDouble2(long bits) {
// Use the upper 54 bits on the assumption they are more random.
// The sign bit generates a value of 0 or 1 for subtraction.
// The next 53 bits generates a positive number in the range [0, 1).
diff --git
a/commons-rng-sampling/src/main/java/org/apache/commons/rng/sampling/shape/UnitBallSampler.java
b/commons-rng-sampling/src/main/java/org/apache/commons/rng/sampling/shape/UnitBallSampler.java
index 75b3ded..3096584 100644
---
a/commons-rng-sampling/src/main/java/org/apache/commons/rng/sampling/shape/UnitBallSampler.java
+++
b/commons-rng-sampling/src/main/java/org/apache/commons/rng/sampling/shape/UnitBallSampler.java
@@ -42,8 +42,13 @@ public abstract class UnitBallSampler implements
SharedStateObjectSampler<double
private static final int TWO_D = 2;
/** The dimension for 3D sampling. */
private static final int THREE_D = 3;
- /** The mask to extract the lower 53-bits from a long. */
- private static final long LOWER_53_BITS = -1L >>> 11;
+ /**
+ * The multiplier to convert the least significant 53-bits of a {@code
long} to a {@code double}.
+ * Taken from o.a.c.rng.core.utils.NumberFactory.
+ *
+ * <p>This is equivalent to 1.0 / (1L << 53).
+ */
+ private static final double DOUBLE_MULTIPLIER = 0x1.0p-53d;
/**
* Sample uniformly from a 1D unit line.
@@ -239,10 +244,11 @@ public abstract class UnitBallSampler implements
SharedStateObjectSampler<double
* @return the double
*/
private static double makeSignedDouble(long bits) {
+ // As per o.a.c.rng.core.utils.NumberFactory.makeDouble(long) but
using a signed
+ // shift of 10 in place of an unsigned shift of 11.
// Use the upper 54 bits on the assumption they are more random.
- // The sign bit generates a value of 0 or 1 for subtraction.
- // The next 53 bits generates a positive number in the range [0, 1).
- // [0, 1) - (0 or 1) => [-1, 1)
- return (((bits >>> 10) & LOWER_53_BITS) * 0x1.0p-53d) - (bits >>> 63);
+ // The sign bit is maintained by the signed shift.
+ // The next 53 bits generates a magnitude in the range [0, 2^53) or
[-2^53, 0).
+ return (bits >> 10) * DOUBLE_MULTIPLIER;
}
}
