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/**
 * 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.codelibs.elasticsearch.taste.common;

import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.AbstractSet;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;

import org.apache.mahout.common.RandomUtils;

import com.google.common.base.Preconditions;

/**
 * @see FastMap
 * @see FastIDSet
 */
public final class FastByIDMap implements Serializable, Cloneable {

    /**
     *
     */
    private static final long serialVersionUID = 1L;

    public static final int NO_MAX_SIZE = Integer.MAX_VALUE;

    private static final float DEFAULT_LOAD_FACTOR = 1.5f;

    /** Dummy object used to represent a key that has been removed. */
    private static final long REMOVED = Long.MAX_VALUE;

    private static final long NULL = Long.MIN_VALUE;

    private long[] keys;

    private V[] values;

    private float loadFactor;

    private int numEntries;

    private int numSlotsUsed;

    private final int maxSize;

    private BitSet recentlyAccessed;

    private final boolean countingAccesses;

    /** Creates a new {@link FastByIDMap} with default capacity. */
    public FastByIDMap() {
        this(2, NO_MAX_SIZE);
    }

    public FastByIDMap(final int size) {
        this(size, NO_MAX_SIZE);
    }

    public FastByIDMap(final int size, final float loadFactor) {
        this(size, NO_MAX_SIZE, loadFactor);
    }

    public FastByIDMap(final int size, final int maxSize) {
        this(size, maxSize, DEFAULT_LOAD_FACTOR);
    }

    /**
     * Creates a new {@link FastByIDMap} whose capacity can accommodate the given number of entries without rehash.
     *
     * @param size desired capacity
     * @param maxSize max capacity
     * @param loadFactor ratio of internal hash table size to current size
     * @throws IllegalArgumentException if size is less than 0, maxSize is less than 1
     *  or at least half of {@link RandomUtils#MAX_INT_SMALLER_TWIN_PRIME}, or
     *  loadFactor is less than 1
     */
    public FastByIDMap(final int size, final int maxSize, final float loadFactor) {
        Preconditions.checkArgument(size >= 0, "size must be at least 0");
        Preconditions.checkArgument(loadFactor >= 1.0f,
                "loadFactor must be at least 1.0");
        this.loadFactor = loadFactor;
        final int max = (int) (RandomUtils.MAX_INT_SMALLER_TWIN_PRIME / loadFactor);
        Preconditions
                .checkArgument(size < max, "size must be less than " + max);
        Preconditions.checkArgument(maxSize >= 1, "maxSize must be at least 1");
        final int hashSize = RandomUtils
                .nextTwinPrime((int) (loadFactor * size));
        keys = new long[hashSize];
        Arrays.fill(keys, NULL);
        values = (V[]) new Object[hashSize];
        this.maxSize = maxSize;
        this.countingAccesses = maxSize != Integer.MAX_VALUE;
        this.recentlyAccessed = countingAccesses ? new BitSet(hashSize) : null;
    }

    /**
     * @see #findForAdd(long)
     */
    private int find(final long key) {
        final int theHashCode = (int) key & 0x7FFFFFFF; // make sure it's positive
        final long[] keys = this.keys;
        final int hashSize = keys.length;
        final int jump = 1 + theHashCode % (hashSize - 2);
        int index = theHashCode % hashSize;
        long currentKey = keys[index];
        while (currentKey != NULL && key != currentKey) {
            index -= index < jump ? jump - hashSize : jump;
            currentKey = keys[index];
        }
        return index;
    }

    /**
     * @see #find(long)
     */
    private int findForAdd(final long key) {
        final int theHashCode = (int) key & 0x7FFFFFFF; // make sure it's positive
        final long[] keys = this.keys;
        final int hashSize = keys.length;
        final int jump = 1 + theHashCode % (hashSize - 2);
        int index = theHashCode % hashSize;
        long currentKey = keys[index];
        while (currentKey != NULL && currentKey != REMOVED && key != currentKey) {
            index -= index < jump ? jump - hashSize : jump;
            currentKey = keys[index];
        }
        if (currentKey != REMOVED) {
            return index;
        }
        // If we're adding, it's here, but, the key might have a value already later
        final int addIndex = index;
        while (currentKey != NULL && key != currentKey) {
            index -= index < jump ? jump - hashSize : jump;
            currentKey = keys[index];
        }
        return key == currentKey ? index : addIndex;
    }

    public V get(final long key) {
        if (key == NULL) {
            return null;
        }
        final int index = find(key);
        if (countingAccesses) {
            recentlyAccessed.set(index);
        }
        return values[index];
    }

    public int size() {
        return numEntries;
    }

    public boolean isEmpty() {
        return numEntries == 0;
    }

    public boolean containsKey(final long key) {
        return key != NULL && key != REMOVED && keys[find(key)] != NULL;
    }

    public boolean containsValue(final Object value) {
        if (value == null) {
            return false;
        }
        for (final V theValue : values) {
            if (theValue != null && value.equals(theValue)) {
                return true;
            }
        }
        return false;
    }

    public V put(final long key, final V value) {
        Preconditions.checkArgument(key != NULL && key != REMOVED);
        Preconditions.checkNotNull(value);
        // If less than half the slots are open, let's clear it up
        if (numSlotsUsed * loadFactor >= keys.length) {
            // If over half the slots used are actual entries, let's grow
            if (numEntries * loadFactor >= numSlotsUsed) {
                growAndRehash();
            } else {
                // Otherwise just rehash to clear REMOVED entries and don't grow
                rehash();
            }
        }
        // Here we may later consider implementing Brent's variation described on page 532
        final int index = findForAdd(key);
        final long keyIndex = keys[index];
        if (keyIndex == key) {
            final V oldValue = values[index];
            values[index] = value;
            return oldValue;
        }
        // If size is limited,
        if (countingAccesses && numEntries >= maxSize) {
            // and we're too large, clear some old-ish entry
            clearStaleEntry(index);
        }
        keys[index] = key;
        values[index] = value;
        numEntries++;
        if (keyIndex == NULL) {
            numSlotsUsed++;
        }
        return null;
    }

    private void clearStaleEntry(int index) {
        while (true) {
            long currentKey;
            do {
                if (index == 0) {
                    index = keys.length - 1;
                } else {
                    index--;
                }
                currentKey = keys[index];
            } while (currentKey == NULL || currentKey == REMOVED);
            if (recentlyAccessed.get(index)) {
                recentlyAccessed.clear(index);
            } else {
                break;
            }
        }
        // Delete the entry
        keys[index] = REMOVED;
        numEntries--;
        values[index] = null;
    }

    public V remove(final long key) {
        if (key == NULL || key == REMOVED) {
            return null;
        }
        final int index = find(key);
        if (keys[index] == NULL) {
            return null;
        } else {
            keys[index] = REMOVED;
            numEntries--;
            final V oldValue = values[index];
            values[index] = null;
            // don't decrement numSlotsUsed
            return oldValue;
        }
        // Could un-set recentlyAccessed's bit but doesn't matter
    }

    public void clear() {
        numEntries = 0;
        numSlotsUsed = 0;
        Arrays.fill(keys, NULL);
        Arrays.fill(values, null);
        if (countingAccesses) {
            recentlyAccessed.clear();
        }
    }

    public LongPrimitiveIterator keySetIterator() {
        return new KeyIterator();
    }

    public Set> entrySet() {
        return new EntrySet();
    }

    public Collection values() {
        return new ValueCollection();
    }

    public void rehash() {
        rehash(RandomUtils.nextTwinPrime((int) (loadFactor * numEntries)));
    }

    private void growAndRehash() {
        if (keys.length * loadFactor >= RandomUtils.MAX_INT_SMALLER_TWIN_PRIME) {
            throw new IllegalStateException("Can't grow any more");
        }
        rehash(RandomUtils.nextTwinPrime((int) (loadFactor * keys.length)));
    }

    private void rehash(final int newHashSize) {
        final long[] oldKeys = keys;
        final V[] oldValues = values;
        numEntries = 0;
        numSlotsUsed = 0;
        if (countingAccesses) {
            recentlyAccessed = new BitSet(newHashSize);
        }
        keys = new long[newHashSize];
        Arrays.fill(keys, NULL);
        values = (V[]) new Object[newHashSize];
        final int length = oldKeys.length;
        for (int i = 0; i < length; i++) {
            final long key = oldKeys[i];
            if (key != NULL && key != REMOVED) {
                put(key, oldValues[i]);
            }
        }
    }

    void iteratorRemove(final int lastNext) {
        if (lastNext >= values.length) {
            throw new NoSuchElementException();
        }
        if (lastNext < 0) {
            throw new IllegalStateException();
        }
        values[lastNext] = null;
        keys[lastNext] = REMOVED;
        numEntries--;
    }

    @Override
    public FastByIDMap clone() {
        FastByIDMap clone;
        try {
            clone = (FastByIDMap) super.clone();
        } catch (final CloneNotSupportedException cnse) {
            throw new AssertionError();
        }
        clone.keys = keys.clone();
        clone.values = values.clone();
        clone.recentlyAccessed = countingAccesses ? new BitSet(keys.length)
                : null;
        return clone;
    }

    @Override
    public String toString() {
        if (isEmpty()) {
            return "{}";
        }
        final StringBuilder result = new StringBuilder();
        result.append('{');
        for (int i = 0; i < keys.length; i++) {
            final long key = keys[i];
            if (key != NULL && key != REMOVED) {
                result.append(key).append('=').append(values[i]).append(',');
            }
        }
        result.setCharAt(result.length() - 1, '}');
        return result.toString();
    }

    @Override
    public int hashCode() {
        int hash = 0;
        final long[] keys = this.keys;
        final int max = keys.length;
        for (int i = 0; i < max; i++) {
            final long key = keys[i];
            if (key != NULL && key != REMOVED) {
                hash = 31 * hash + ((int) (key >> 32) ^ (int) key);
                hash = 31 * hash + values[i].hashCode();
            }
        }
        return hash;
    }

    @Override
    public boolean equals(final Object other) {
        if (!(other instanceof FastByIDMap)) {
            return false;
        }
        final FastByIDMap otherMap = (FastByIDMap) other;
        final long[] otherKeys = otherMap.keys;
        final V[] otherValues = otherMap.values;
        final int length = keys.length;
        final int otherLength = otherKeys.length;
        final int max = Math.min(length, otherLength);

        int i = 0;
        while (i < max) {
            final long key = keys[i];
            final long otherKey = otherKeys[i];
            if (key == NULL || key == REMOVED) {
                if (otherKey != NULL && otherKey != REMOVED) {
                    return false;
                }
            } else {
                if (key != otherKey || !values[i].equals(otherValues[i])) {
                    return false;
                }
            }
            i++;
        }
        while (i < length) {
            final long key = keys[i];
            if (key != NULL && key != REMOVED) {
                return false;
            }
            i++;
        }
        while (i < otherLength) {
            final long key = otherKeys[i];
            if (key != NULL && key != REMOVED) {
                return false;
            }
            i++;
        }
        return true;
    }

    private final class KeyIterator extends AbstractLongPrimitiveIterator {

        private int position;

        private int lastNext = -1;

        @Override
        public boolean hasNext() {
            goToNext();
            return position < keys.length;
        }

        @Override
        public long nextLong() {
            goToNext();
            lastNext = position;
            if (position >= keys.length) {
                throw new NoSuchElementException();
            }
            return keys[position++];
        }

        @Override
        public long peek() {
            goToNext();
            if (position >= keys.length) {
                throw new NoSuchElementException();
            }
            return keys[position];
        }

        private void goToNext() {
            final int length = values.length;
            while (position < length && values[position] == null) {
                position++;
            }
        }

        @Override
        public void remove() {
            iteratorRemove(lastNext);
        }

        @Override
        public void skip(final int n) {
            position += n;
        }

    }

    private final class EntrySet extends AbstractSet> {

        @Override
        public int size() {
            return FastByIDMap.this.size();
        }

        @Override
        public boolean isEmpty() {
            return FastByIDMap.this.isEmpty();
        }

        @Override
        public boolean contains(final Object o) {
            return containsKey((Long) o);
        }

        @Override
        public Iterator> iterator() {
            return new EntryIterator();
        }

        @Override
        public boolean add(final Map.Entry t) {
            throw new UnsupportedOperationException();
        }

        @Override
        public boolean remove(final Object o) {
            throw new UnsupportedOperationException();
        }

        @Override
        public boolean addAll(final Collection> ts) {
            throw new UnsupportedOperationException();
        }

        @Override
        public boolean retainAll(final Collection objects) {
            throw new UnsupportedOperationException();
        }

        @Override
        public boolean removeAll(final Collection objects) {
            throw new UnsupportedOperationException();
        }

        @Override
        public void clear() {
            FastByIDMap.this.clear();
        }

        private final class MapEntry implements Map.Entry {

            private final int index;

            private MapEntry(final int index) {
                this.index = index;
            }

            @Override
            public Long getKey() {
                return keys[index];
            }

            @Override
            public V getValue() {
                return values[index];
            }

            @Override
            public V setValue(final V value) {
                Preconditions.checkArgument(value != null);

                final V oldValue = values[index];
                values[index] = value;
                return oldValue;
            }
        }

        private final class EntryIterator implements
                Iterator> {

            private int position;

            private int lastNext = -1;

            @Override
            public boolean hasNext() {
                goToNext();
                return position < keys.length;
            }

            @Override
            public Map.Entry next() {
                goToNext();
                lastNext = position;
                if (position >= keys.length) {
                    throw new NoSuchElementException();
                }
                return new MapEntry(position++);
            }

            private void goToNext() {
                final int length = values.length;
                while (position < length && values[position] == null) {
                    position++;
                }
            }

            @Override
            public void remove() {
                iteratorRemove(lastNext);
            }
        }

    }

    private final class ValueCollection extends AbstractCollection {

        @Override
        public int size() {
            return FastByIDMap.this.size();
        }

        @Override
        public boolean isEmpty() {
            return FastByIDMap.this.isEmpty();
        }

        @Override
        public boolean contains(final Object o) {
            return containsValue(o);
        }

        @Override
        public Iterator iterator() {
            return new ValueIterator();
        }

        @Override
        public boolean add(final V v) {
            throw new UnsupportedOperationException();
        }

        @Override
        public boolean remove(final Object o) {
            throw new UnsupportedOperationException();
        }

        @Override
        public boolean addAll(final Collection vs) {
            throw new UnsupportedOperationException();
        }

        @Override
        public boolean removeAll(final Collection objects) {
            throw new UnsupportedOperationException();
        }

        @Override
        public boolean retainAll(final Collection objects) {
            throw new UnsupportedOperationException();
        }

        @Override
        public void clear() {
            FastByIDMap.this.clear();
        }

        private final class ValueIterator implements Iterator {

            private int position;

            private int lastNext = -1;

            @Override
            public boolean hasNext() {
                goToNext();
                return position < values.length;
            }

            @Override
            public V next() {
                goToNext();
                lastNext = position;
                if (position >= values.length) {
                    throw new NoSuchElementException();
                }
                return values[position++];
            }

            private void goToNext() {
                final int length = values.length;
                while (position < length && values[position] == null) {
                    position++;
                }
            }

            @Override
            public void remove() {
                iteratorRemove(lastNext);
            }

        }

    }
}




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