[GitHub] [commons-rng] aherbert commented on a change in pull request #56: RNG: 84 - Added members of the PCG suite of generators.

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aherbert commented on a change in pull request #56: RNG: 84 - Added members of the PCG suite of generators.
URL: https://github.com/apache/commons-rng/pull/56#discussion_r305631106
 
 

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 File path: commons-rng-core/src/main/java/org/apache/commons/rng/core/source32/AbstractPcg6432.java
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 @@ -0,0 +1,105 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.rng.core.source32;
+
+import org.apache.commons.rng.core.util.NumberFactory;
+/**
+ * This class aids in implementation of the PCG suite of generators, a family of
+ * simple fast space-efficient statistically good algorithms for random number generation.
+ * @see <a href="http://www.pcg-random.org/">
+ *  PCG, A Family of Better Random Number Generators</a>
+ * @since 1.3
+ */
+abstract class AbstractPcg6432 extends IntProvider {
+    /** Size of the state array. */
+    private static final int SEED_SIZE = 2;
+
+    /** Displays the current state. */
+    private long state;
+
+    /** Used as a part of the LCG. */
+    private long increment;
+
+    /**
+     * Creates a new instance.
+     *
+     * @param seed Initial seed.
+     * If the length is larger than 2, only the first 2 elements will
+     * be used; if smaller, the remaining elements will be automatically set.
+     */
+    AbstractPcg6432(long[] seed) {
+        if (seed.length < SEED_SIZE) {
+            final long[] tmp = new long[SEED_SIZE];
+            fillState(tmp, seed);
+            setSeedInternal(tmp);
+        } else {
+            setSeedInternal(seed);
+        }
+    }
+
+    /**
+     * Modifies input parameters into current state.
+     * @param seed the new seed.
+     */
+    private void setSeedInternal(long[] seed) {
+        this.increment = (seed[1] << 1) | 1;
+        this.state = bump(seed[0] + this.increment);
+    }
+
+    /**
+     * Provides the next state of the LCG.
+     * @param input - The previous state of the generator.
+     * @return Next state of the LCG.
+     */
+    private long bump(long input) {
+        return input * 6364136223846793005L + increment;
+    }
+
+    /** {@inheritDoc} */
+    @Override
+    public int next() {
+        final long x = state;
+        state = bump(state);
+        return transform(x);
+    }
+
+    /**
+     * The transformation function shall vary with respect to different generators.
+     * @param x The input.
+     * @return The output of the generator.
+     */
+    protected abstract int transform(long x);
+
+    /** {@inheritDoc} */
+    @Override
+    protected byte[] getStateInternal() {
+        return composeStateInternal(NumberFactory.makeByteArray(
+                new long[] {state, increment >>> 1}),
+                super.getStateInternal());
+    }
+
+    /** {@inheritDoc} */
+    @Override
+    protected void setStateInternal(byte[] s) {
+        final byte[][] c = splitStateInternal(s, SEED_SIZE * 8);
+        long[] tempseed;
 
 Review comment:
   This can be a final variable and assigned in the declaration.

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