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.bcel.generic;
018
019import java.util.Arrays;
020
021/**
022 * SWITCH - Branch depending on int value, generates either LOOKUPSWITCH or TABLESWITCH instruction, depending on
023 * whether the match values (int[]) can be sorted with no gaps between the numbers.
024 */
025public final class SWITCH implements CompoundInstruction {
026
027    /**
028     * @return match is sorted in ascending order with no gap bigger than maxGap?
029     */
030    private static boolean matchIsOrdered(final int[] match, final int matchLength, final int maxGap) {
031        for (int i = 1; i < matchLength; i++) {
032            if (match[i] - match[i - 1] > maxGap) {
033                return false;
034            }
035        }
036        return true;
037    }
038
039    /**
040     * Sorts match and targets array with QuickSort.
041     */
042    private static void sort(final int l, final int r, final int[] match, final InstructionHandle[] targets) {
043        int i = l;
044        int j = r;
045        int h;
046        final int m = match[l + r >>> 1];
047        InstructionHandle h2;
048        do {
049            while (match[i] < m) {
050                i++;
051            }
052            while (m < match[j]) {
053                j--;
054            }
055            if (i <= j) {
056                h = match[i];
057                match[i] = match[j];
058                match[j] = h; // Swap elements
059                h2 = targets[i];
060                targets[i] = targets[j];
061                targets[j] = h2; // Swap instructions, too
062                i++;
063                j--;
064            }
065        } while (i <= j);
066        if (l < j) {
067            sort(l, j, match, targets);
068        }
069        if (i < r) {
070            sort(i, r, match, targets);
071        }
072    }
073
074    private final Select instruction;
075
076    public SWITCH(final int[] match, final InstructionHandle[] targets, final InstructionHandle target) {
077        this(match, targets, target, 1);
078    }
079
080    /**
081     * Template for switch() constructs. If the match array can be sorted in ascending order with gaps no larger than
082     * maxGap between the numbers, a TABLESWITCH instruction is generated, and a LOOKUPSWITCH otherwise. The former may be
083     * more efficient, but needs more space.
084     *
085     * Note, that the key array always will be sorted, though we leave the original arrays unaltered.
086     *
087     * @param match array of match values (case 2: ... case 7: ..., etc.)
088     * @param targets the instructions to be branched to for each case
089     * @param target the default target
090     * @param maxGap maximum gap that may between case branches
091     */
092    public SWITCH(final int[] match, final InstructionHandle[] targets, final InstructionHandle target, final int maxGap) {
093        final int[] matchClone = match.clone();
094        final InstructionHandle[] targetsClone = targets.clone();
095        final int matchLength = match.length;
096        if (matchLength < 2) {
097            instruction = new TABLESWITCH(match, targets, target);
098        } else {
099            sort(0, matchLength - 1, matchClone, targetsClone);
100            if (matchIsOrdered(matchClone, matchLength, maxGap)) {
101                final int maxSize = matchLength + matchLength * maxGap;
102                final int[] mVec = new int[maxSize];
103                final InstructionHandle[] tVec = new InstructionHandle[maxSize];
104                int count = 1;
105                mVec[0] = match[0];
106                tVec[0] = targets[0];
107                for (int i = 1; i < matchLength; i++) {
108                    final int prev = match[i - 1];
109                    final int gap = match[i] - prev;
110                    for (int j = 1; j < gap; j++) {
111                        mVec[count] = prev + j;
112                        tVec[count] = target;
113                        count++;
114                    }
115                    mVec[count] = match[i];
116                    tVec[count] = targets[i];
117                    count++;
118                }
119                instruction = new TABLESWITCH(Arrays.copyOf(mVec, count), Arrays.copyOf(tVec, count), target);
120            } else {
121                instruction = new LOOKUPSWITCH(matchClone, targetsClone, target);
122            }
123        }
124    }
125
126    public Instruction getInstruction() {
127        return instruction;
128    }
129
130    @Override
131    public InstructionList getInstructionList() {
132        return new InstructionList(instruction);
133    }
134}