optimized ASR version

gistfile1.java

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package org.jruby.util;

import java.math.BigInteger;
import java.util.Arrays;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.concurrent.atomic.AtomicReference;

public class NewRandom {
    public static int N = 624;
    private static int M = 397;
    private static int MATRIX_A = 0x9908b0df; /* constant vector a */
    private static int UMASK = 0x80000000; /* most significant w-r bits */
    private static int LMASK = 0x7fffffff; /* least significant r bits */

    private static int MIXBITS(int u, int v) {
        return (u & UMASK) | (v & LMASK);
    }

    private static int TWIST(int u, int v) {
        return (MIXBITS(u, v) >>> 1) ^ (((v & 1) != 0) ? MATRIX_A : 0);
    }

    private final MyAtomicStampedReference<int[]> holder = new MyAtomicStampedReference<int[]>(new int[N], 1);

    public NewRandom(int s) {
        initGenrand(s);
    }

    public NewRandom(int[] initKey) {
        holder.set(initByArray(initKey), 1);
    }

    public NewRandom(NewRandom orig) {
        Pair<int[]> pair = orig.holder.pair();

        holder.set(Arrays.copyOf(pair.reference, N), pair.stamp);
    }

    public NewRandom(int[] state, int left) {
        if (state.length != this.holder.getReference().length) {
            throw new IllegalStateException("wrong state length: " + state.length);
        }
        // use existing initial state[]
        System.arraycopy(state, 0, this.holder.getReference(), 0, N);
        this.holder.set(this.holder.getReference(), left);
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        } else if (!(obj instanceof NewRandom)) {
            return false;
        }
        return ((NewRandom) obj).holder.equals(this.holder);
    }

    @Override
    public int hashCode() {
        // Using 17 as the initializer, 37 as the multiplier.
        return (629 + holder.getStamp()) * 37 + holder.hashCode();
    }

    private static int[] initGenrand(int s) {
        int[] state = new int[N];
        state[0] = s;
        for (int j = 1; j < N; j++) {
            state[j] = (1812433253 * (state[j - 1] ^ (state[j - 1] >>> 30)) + j);
        }
        return state;
    }

    private static int[] initByArray(int[] initKey) {
        int[] newState = initGenrand(19650218);
        int len = initKey.length;
        int i = 1;
        int j = 0;
        int k = N > len ? N : len;
        int[] state = Arrays.copyOf(newState, N);
        for (; k > 0; k--) {
            state[i] = (state[i] ^ ((state[i - 1] ^ (state[i - 1] >>> 30)) * 1664525)) + initKey[j]
                    + j;
            i++;
            j++;
            if (i >= N) {
                state[0] = state[N - 1];
                i = 1;
            }
            if (j >= len) {
                j = 0;
            }
        }
        for (k = N - 1; k > 0; k--) {
            state[i] = (state[i] ^ ((state[i - 1] ^ (state[i - 1] >>> 30)) * 1566083941)) - i;
            i++;
            if (i >= N) {
                state[0] = state[N - 1];
                i = 1;
            }
        }
        state[0] = 0x80000000;

        return state;
    }

    private static void nextState(int[] state) {
        int p = 0;

        for (int j = N - M + 1; --j > 0; p++) {
            state[p] = state[p + M] ^ TWIST(state[p + 0], state[p + 1]);
        }

        for (int j = M; --j > 0; p++) {
            state[p] = state[p + M - N] ^ TWIST(state[p + 0], state[p + 1]);
        }

        state[p] = state[p + M - N] ^ TWIST(state[p + 0], state[0]);
    }

    public int genrandInt32() {
        int y;
        int[] state;
        int[] stateCopy = null;
        int left;


        while (true) {
            state = holder.getReference();
            left = holder.getStamp();
            if (left > 1) {
                int nl = left - 1;
                if (holder.compareAndSet(state, left, nl)) {
                    // success! update left to the actual value, and break out
                    left = nl;
                    break;
                } else {
                    // someone beaten us to it, respin
                }
            } else {
                // try to update
                // $left should be exactly one at this point
                assert left == 1;

                // nextState() should be idempotent
                if (stateCopy == null) stateCopy = Arrays.copyOf(state, N); // only create new array once
                else System.arraycopy(state, 0, stateCopy, 0, N);
                nextState(stateCopy);

                // allow only one CAS, don't care about the result, respin
                holder.compareAndSet(state, stateCopy, 1, N);
            }
        }

        y = state[N - left];

        /* Tempering */
        y ^= (y >>> 11);
        y ^= (y << 7) & 0x9d2c5680L;
        y ^= (y << 15) & 0xefc60000L;
        y ^= (y >>> 18);

        return y;
    }

    public static class MyAtomicStampedReference<V> extends AtomicReference<Pair<V>> {

        public MyAtomicStampedReference(V initialRef, int initialStamp) {
            super(Pair.of(initialRef, initialStamp));
        }

        public boolean compareAndSet(V expectedRef, V newRef, int expectedStamp, int newStamp) {
            Pair<V> current = super.get();
            return
                    expectedRef == current.reference &&
                            expectedStamp == current.stamp &&
                            ((newRef == current.reference &&
                                    newStamp == current.stamp) ||
                                    super.compareAndSet(current, Pair.of(newRef, newStamp)));


        }

        public boolean compareAndSet(V expectedRef, int expectedStamp, int newStamp) {
            Pair<V> current = super.get();
            return (expectedRef == current.reference) && current.compareAndSwapStamp(expectedStamp, newStamp);
        }

        public void set(V newRef, int newStamp) {
            super.set(Pair.of(newRef, newStamp));
        }

        public V getReference() {
            return super.get().reference;
        }

        public int getStamp() {
            return super.get().stamp;
        }

        public Pair<V> pair() {
            Pair<V> vPair = super.get();
            return Pair.of(vPair.reference, vPair.stamp);
        }
    }

    public static class Pair<T> {
        final T reference;
        volatile int stamp;

        private static final AtomicIntegerFieldUpdater<Pair> UPDATER = AtomicIntegerFieldUpdater.newUpdater(Pair.class, "stamp");

        private Pair(T reference, int stamp) {
            this.reference = reference;
            this.stamp = stamp;
        }

        private boolean compareAndSwapStamp(int expected, int newStamp) {
            return UPDATER.compareAndSet(this, expected, newStamp);
        }

        static <T> Pair<T> of(T reference, int stamp) {
            return new Pair<T>(reference, stamp);
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) {
                return true;
            }
            if (o == null || getClass() != o.getClass()) {
                return false;
            }

            Pair pair = (Pair) o;

            if (stamp != pair.stamp) {
                return false;
            }
            if (reference != null ? !reference.equals(pair.reference) : pair.reference != null) {
                return false;
            }

            return true;
        }

        @Override
        public int hashCode() {
            int result = reference != null ? reference.hashCode() : 0;
            result = 31 * result + stamp;
            return result;
        }
    }



    public double genrandReal() {
        int a = genrandInt32() >>> 5;
        int b = genrandInt32() >>> 6;
        return (a * 67108864.0 + b) * (1.0 / 9007199254740992.0);
    }

    public double genrandReal2() {
        int a = genrandInt32();
        int b = genrandInt32();
        return intPairToRealInclusive(a, b);
    }

    private static final BigInteger INTPAIR_CONST = BigInteger.valueOf((1L << 53) + 1);
    private static final double LDEXP_CONST = Math.pow(2.0, -53);

    // c: ldexp((a<< 32)|b) * ((1<<53)+1) >> 64, -53)
    // TODO: not enough prec...
    private double intPairToRealInclusive(int a, int b) {
        BigInteger c = BigInteger.valueOf(a & 0xffffffffL);
        BigInteger d = BigInteger.valueOf(b & 0xffffffffL);
        return c.shiftLeft(32).or(d).multiply(INTPAIR_CONST).shiftRight(64).doubleValue()
                * LDEXP_CONST;
    }

    public int[] getState() {
        return holder.getReference();
    }

    public int getLeft() {
        return holder.getStamp();
    }

}