    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.collections4.bloomfilter;
    018
    019import java.util.function.IntPredicate;
    020
    021/**
    022 * A convenience class for Hasher implementations to filter out duplicate indices.
    023 *
    024 * <p><em>If the index is negative the behavior is not defined.</em></p>
    025 *
    026 * <p>This is conceptually a unique filter implemented as an {@link IntPredicate}.</p>
    027 *
    028 * @since 4.5.0-M1
    029 */
    030public final class IndexFilter {
    031
    032    /**
    033     * An IndexTracker implementation that uses an array of integers to track whether or not a
    034     * number has been seen. Suitable for Shapes that have few hash functions.
    035     * @since 4.5.0
    036     */
    037    static class ArrayTracker implements IntPredicate {
    038        private final int[] seen;
    039        private int populated;
    040
    041        /**
    042         * Constructs the tracker based on the shape.
    043         * @param shape the shape to build the tracker for.
    044         */
    045        ArrayTracker(final Shape shape) {
    046            seen = new int[shape.getNumberOfHashFunctions()];
    047        }
    048
    049        @Override
    050        public boolean test(final int number) {
    051            if (number < 0) {
    052                throw new IndexOutOfBoundsException("number may not be less than zero. " + number);
    053            }
    054            for (int i = 0; i < populated; i++) {
    055                if (seen[i] == number) {
    056                    return false;
    057                }
    058            }
    059            seen[populated++] = number;
    060            return true;
    061        }
    062    }
    063
    064    /**
    065     * An IndexTracker implementation that uses an array of bit maps to track whether or not a
    066     * number has been seen.
    067     */
    068    static class BitMapTracker implements IntPredicate {
    069        private final long[] bits;
    070
    071        /**
    072         * Constructs a bit map based tracker for the specified shape.
    073         * @param shape The shape that is being generated.
    074         */
    075        BitMapTracker(final Shape shape) {
    076            bits = BitMaps.newBitMap(shape);
    077        }
    078
    079        @Override
    080        public boolean test(final int number) {
    081            final boolean retval = !BitMaps.contains(bits, number);
    082            BitMaps.set(bits, number);
    083            return retval;
    084        }
    085    }
    086
    087    /**
    088     * Creates an instance optimized for the specified shape.
    089     *
    090     * @param shape The shape that is being generated.
    091     * @param consumer The consumer to accept the values.
    092     * @return an IndexFilter optimized for the specified shape.
    093     */
    094    public static IntPredicate create(final Shape shape, final IntPredicate consumer) {
    095        return new IndexFilter(shape, consumer)::test;
    096    }
    097
    098    private final IntPredicate tracker;
    099
    100    private final int size;
    101
    102    private final IntPredicate consumer;
    103
    104    /**
    105     * Creates an instance optimized for the specified shape.
    106     *
    107     * @param shape The shape that is being generated.
    108     * @param consumer The consumer to accept the values.
    109     */
    110    private IndexFilter(final Shape shape, final IntPredicate consumer) {
    111        this.size = shape.getNumberOfBits();
    112        this.consumer = consumer;
    113        if (BitMaps.numberOfBitMaps(shape) * Long.BYTES < (long) shape.getNumberOfHashFunctions() * Integer.BYTES) {
    114            this.tracker = new BitMapTracker(shape);
    115        } else {
    116            this.tracker = new ArrayTracker(shape);
    117        }
    118    }
    119
    120    /**
    121     * Test if the number should be processed by the {@code consumer}.
    122     *
    123     * <p>If the number has <em>not</em> been seen before it is passed to the {@code consumer} and the result returned.
    124     * If the number has been seen before the {@code consumer} is not called and {@code true} returned.</p>
    125     *
    126     * <p><em>If the input is not in the range [0,size) an IndexOutOfBoundsException exception is thrown.</em></p>
    127     *
    128     * @param number the number to check.
    129     * @return {@code true} if processing should continue, {@code false} otherwise.
    130     */
    131    public boolean test(final int number) {
    132        if (number >= size) {
    133            throw new IndexOutOfBoundsException(String.format("number too large %d >= %d", number, size));
    134        }
    135        if (tracker.test(number)) {
    136            return consumer.test(number);
    137        }
    138        return true;
    139    }
    140}