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