src/main/java/org/apache/bcel/generic/SWITCH.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.bcel.generic;

import java.util.Arrays;

/**
 * SWITCH - Branch depending on int value, generates either LOOKUPSWITCH or TABLESWITCH instruction, depending on
 * whether the match values (int[]) can be sorted with no gaps between the numbers.
 */
public final class SWITCH implements CompoundInstruction {

    /**
     * @return match is sorted in ascending order with no gap bigger than maxGap?
     */
    private static boolean matchIsOrdered(final int[] match, final int matchLength, final int maxGap) {
        for (int i = 1; i < matchLength; i++) {
            if (match[i] - match[i - 1] > maxGap) {
                return false;
            }
        }
        return true;
    }

    /**
     * Sorts match and targets array with QuickSort.
     */
    private static void sort(final int l, final int r, final int[] match, final InstructionHandle[] targets) {
        int i = l;
        int j = r;
        int h;
        final int m = match[l + r >>> 1];
        InstructionHandle h2;
        do {
            while (match[i] < m) {
                i++;
            }
            while (m < match[j]) {
                j--;
            }
            if (i <= j) {
                h = match[i];
                match[i] = match[j];
                match[j] = h; // Swap elements
                h2 = targets[i];
                targets[i] = targets[j];
                targets[j] = h2; // Swap instructions, too
                i++;
                j--;
            }
        } while (i <= j);
        if (l < j) {
            sort(l, j, match, targets);
        }
        if (i < r) {
            sort(i, r, match, targets);
        }
    }

    private final Select instruction;

    public SWITCH(final int[] match, final InstructionHandle[] targets, final InstructionHandle target) {
        this(match, targets, target, 1);
    }

    /**
     * Template for switch() constructs. If the match array can be sorted in ascending order with gaps no larger than
     * maxGap between the numbers, a TABLESWITCH instruction is generated, and a LOOKUPSWITCH otherwise. The former may be
     * more efficient, but needs more space.
     *
     * Note, that the key array always will be sorted, though we leave the original arrays unaltered.
     *
     * @param match array of match values (case 2: ... case 7: ..., etc.).
     * @param targets the instructions to be branched to for each case.
     * @param target the default target.
     * @param maxGap maximum gap that may between case branches.
     */
    public SWITCH(final int[] match, final InstructionHandle[] targets, final InstructionHandle target, final int maxGap) {
        final int[] matchClone = match.clone();
        final InstructionHandle[] targetsClone = targets.clone();
        final int matchLength = match.length;
        if (matchLength < 2) {
            instruction = new TABLESWITCH(match, targets, target);
        } else {
            sort(0, matchLength - 1, matchClone, targetsClone);
            if (matchIsOrdered(matchClone, matchLength, maxGap)) {
                final int maxSize = matchLength + matchLength * maxGap;
                final int[] mVec = new int[maxSize];
                final InstructionHandle[] tVec = new InstructionHandle[maxSize];
                int count = 1;
                mVec[0] = match[0];
                tVec[0] = targets[0];
                for (int i = 1; i < matchLength; i++) {
                    final int prev = match[i - 1];
                    final int gap = match[i] - prev;
                    for (int j = 1; j < gap; j++) {
                        mVec[count] = prev + j;
                        tVec[count] = target;
                        count++;
                    }
                    mVec[count] = match[i];
                    tVec[count] = targets[i];
                    count++;
                }
                instruction = new TABLESWITCH(Arrays.copyOf(mVec, count), Arrays.copyOf(tVec, count), target);
            } else {
                instruction = new LOOKUPSWITCH(matchClone, targetsClone, target);
            }
        }
    }

    public Instruction getInstruction() {
        return instruction;
    }

    @Override
    public InstructionList getInstructionList() {
        return new InstructionList(instruction);
    }
}