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.trie.analyzer;
018
019import org.apache.commons.collections4.trie.KeyAnalyzer;
020
021/**
022 * An {@link KeyAnalyzer} for {@link String}s.
023 *
024 * @since 4.0
025 * @version $Id: StringKeyAnalyzer.html 972421 2015-11-14 20:00:04Z tn $
026 */
027public class StringKeyAnalyzer extends KeyAnalyzer<String> {
028
029    private static final long serialVersionUID = -7032449491269434877L;
030
031    /** A singleton instance of {@link StringKeyAnalyzer}. */
032    public static final StringKeyAnalyzer INSTANCE = new StringKeyAnalyzer();
033
034    /** The number of bits per {@link Character}. */
035    public static final int LENGTH = Character.SIZE;
036
037    /** A bit mask where the first bit is 1 and the others are zero. */
038    private static final int MSB = 0x8000;
039
040    /** Returns a bit mask where the given bit is set. */
041    private static int mask(final int bit) {
042        return MSB >>> bit;
043    }
044
045    @Override
046    public int bitsPerElement() {
047        return LENGTH;
048    }
049
050    @Override
051    public int lengthInBits(final String key) {
052        return key != null ? key.length() * LENGTH : 0;
053    }
054
055    @Override
056    public int bitIndex(final String key, final int offsetInBits, final int lengthInBits,
057                        final String other, final int otherOffsetInBits, final int otherLengthInBits) {
058
059        boolean allNull = true;
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 = beginIndex2 + otherLengthInBits / LENGTH;
071
072        final int length = Math.max(endIndex1, endIndex2);
073
074        // Look at each character, and if they're different
075        // then figure out which bit makes the difference
076        // and return it.
077        char k = 0, f = 0;
078        for(int i = 0; i < length; i++) {
079            final int index1 = beginIndex1 + i;
080            final int index2 = beginIndex2 + i;
081
082            if (index1 >= endIndex1) {
083                k = 0;
084            } else {
085                k = key.charAt(index1);
086            }
087
088            if (other == null || index2 >= endIndex2) {
089                f = 0;
090            } else {
091                f = other.charAt(index2);
092            }
093
094            if (k != f) {
095               final int x = k ^ f;
096               return i * LENGTH + Integer.numberOfLeadingZeros(x) - LENGTH;
097            }
098
099            if (k != 0) {
100                allNull = false;
101            }
102        }
103
104        // All bits are 0
105        if (allNull) {
106            return KeyAnalyzer.NULL_BIT_KEY;
107        }
108
109        // Both keys are equal
110        return KeyAnalyzer.EQUAL_BIT_KEY;
111    }
112
113    @Override
114    public boolean isBitSet(final String key, final int bitIndex, final int lengthInBits) {
115        if (key == null || bitIndex >= lengthInBits) {
116            return false;
117        }
118
119        final int index = bitIndex / LENGTH;
120        final int bit = bitIndex % LENGTH;
121
122        return (key.charAt(index) & mask(bit)) != 0;
123    }
124
125    @Override
126    public boolean isPrefix(final String prefix, final int offsetInBits,
127                            final int lengthInBits, final String key) {
128        if (offsetInBits % LENGTH != 0 || lengthInBits % LENGTH != 0) {
129            throw new IllegalArgumentException(
130                    "Cannot determine prefix outside of Character boundaries");
131        }
132
133        final String s1 = prefix.substring(offsetInBits / LENGTH, lengthInBits / LENGTH);
134        return key.startsWith(s1);
135    }
136}