    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 *      https://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.trie.analyzer;
    018
    019import org.apache.commons.collections4.trie.KeyAnalyzer;
    020
    021/**
    022 * An {@link KeyAnalyzer} for {@link String}s.
    023 * <p>
    024 * This class is stateless.
    025 * </p>
    026 *
    027 * @since 4.0
    028 */
    029public class StringKeyAnalyzer extends KeyAnalyzer<String> {
    030
    031    private static final long serialVersionUID = -7032449491269434877L;
    032
    033    /** A singleton instance of {@link StringKeyAnalyzer}. */
    034    public static final StringKeyAnalyzer INSTANCE = new StringKeyAnalyzer();
    035
    036    /** The number of bits per {@link Character} plus a presence bit. */
    037    public static final int LENGTH = Character.SIZE + 1;
    038
    039    /** A bit mask where the first bit is 1 and the others are zero. */
    040    private static final int MSB = 0x8000;
    041
    042    /** Returns a bit mask where the given bit is set. */
    043    private static int mask(final int bit) {
    044        return MSB >>> bit;
    045    }
    046
    047    /**
    048     * Constructs a new instance.
    049     *
    050     * @deprecated Use {@link #INSTANCE}.
    051     */
    052    @Deprecated
    053    public StringKeyAnalyzer() {
    054        // empty
    055    }
    056
    057    @Override
    058    public int bitIndex(final String key, final int offsetInBits, final int lengthInBits,
    059                        final String other, final int otherOffsetInBits, final int otherLengthInBits) {
    060
    061        if (offsetInBits % LENGTH != 0 || otherOffsetInBits % LENGTH != 0
    062                || lengthInBits % LENGTH != 0 || otherLengthInBits % LENGTH != 0) {
    063            throw new IllegalArgumentException("The offsets and lengths must be at Character boundaries");
    064        }
    065
    066        final int beginIndex1 = offsetInBits / LENGTH;
    067        final int beginIndex2 = otherOffsetInBits / LENGTH;
    068
    069        final int endIndex1 = beginIndex1 + lengthInBits / LENGTH;
    070        final int endIndex2 = other == null ? beginIndex2 : beginIndex2 + otherLengthInBits / LENGTH;
    071
    072        final int length = Math.max(endIndex1, endIndex2);
    073
    074        for (int i = 0; i < length; i++) {
    075            final int index1 = beginIndex1 + i;
    076            final int index2 = beginIndex2 + i;
    077
    078            if (index1 < endIndex1 && other != null && index2 < endIndex2) {
    079                final char k = key.charAt(index1);
    080                final char f = other.charAt(index2);
    081
    082                if (k != f) {
    083                    final int x = k ^ f;
    084                    return i * LENGTH + 1 + Integer.numberOfLeadingZeros(x) - (LENGTH - 1);
    085                }
    086            } else {
    087                // One has ended, the other has not. They differ at the presence bit of this block.
    088                return i * LENGTH;
    089            }
    090        }
    091
    092        if (lengthInBits == 0 && (other == null || otherLengthInBits == 0)) {
    093            return NULL_BIT_KEY;
    094        }
    095
    096        // Both keys are equal
    097        return EQUAL_BIT_KEY;
    098    }
    099
    100    @Override
    101    public int bitsPerElement() {
    102        return LENGTH;
    103    }
    104
    105    @Override
    106    public boolean isBitSet(final String key, final int bitIndex, final int lengthInBits) {
    107        if (key == null || bitIndex >= lengthInBits) {
    108            return false;
    109        }
    110
    111        final int index = bitIndex / LENGTH;
    112        final int bit = bitIndex % LENGTH;
    113
    114        if (bit == 0) {
    115            return true;
    116        }
    117        return (key.charAt(index) & mask(bit - 1)) != 0;
    118    }
    119
    120    @Override
    121    public boolean isPrefix(final String prefix, final int offsetInBits,
    122                            final int lengthInBits, final String key) {
    123        if (offsetInBits % LENGTH != 0 || lengthInBits % LENGTH != 0) {
    124            throw new IllegalArgumentException(
    125                    "Cannot determine prefix outside of Character boundaries");
    126        }
    127
    128        final String s1 = prefix.substring(offsetInBits / LENGTH, lengthInBits / LENGTH);
    129        return key.startsWith(s1);
    130    }
    131
    132    @Override
    133    public int lengthInBits(final String key) {
    134        return key != null ? key.length() * LENGTH : 0;
    135    }
    136}