Source code

    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 *
    017 */
    018package org.apache.bcel.generic;
    019
    020/**
    021 * SWITCH - Branch depending on int value, generates either LOOKUPSWITCH or
    022 * TABLESWITCH instruction, depending on whether the match values (int[]) can be
    023 * sorted with no gaps between the numbers.
    024 *
    025 */
    026public final class SWITCH implements CompoundInstruction {
    027
    028    private int[] match;
    029    private InstructionHandle[] targets;
    030    private Select instruction;
    031    private int match_length;
    032
    033
    034    /**
    035     * Template for switch() constructs. If the match array can be
    036     * sorted in ascending order with gaps no larger than max_gap
    037     * between the numbers, a TABLESWITCH instruction is generated, and
    038     * a LOOKUPSWITCH otherwise. The former may be more efficient, but
    039     * needs more space.
    040     *
    041     * Note, that the key array always will be sorted, though we leave
    042     * the original arrays unaltered.
    043     *
    044     * @param match array of match values (case 2: ... case 7: ..., etc.)
    045     * @param targets the instructions to be branched to for each case
    046     * @param target the default target
    047     * @param max_gap maximum gap that may between case branches
    048     */
    049    public SWITCH(final int[] match, final InstructionHandle[] targets, final InstructionHandle target, final int max_gap) {
    050        this.match = match.clone();
    051        this.targets = targets.clone();
    052        if ((match_length = match.length) < 2) {
    053            instruction = new TABLESWITCH(match, targets, target);
    054        } else {
    055            sort(0, match_length - 1);
    056            if (matchIsOrdered(max_gap)) {
    057                fillup(max_gap, target);
    058                instruction = new TABLESWITCH(this.match, this.targets, target);
    059            } else {
    060                instruction = new LOOKUPSWITCH(this.match, this.targets, target);
    061            }
    062        }
    063    }
    064
    065
    066    public SWITCH(final int[] match, final InstructionHandle[] targets, final InstructionHandle target) {
    067        this(match, targets, target, 1);
    068    }
    069
    070
    071    private void fillup( final int max_gap, final InstructionHandle target ) {
    072        final int max_size = match_length + match_length * max_gap;
    073        final int[] m_vec = new int[max_size];
    074        final InstructionHandle[] t_vec = new InstructionHandle[max_size];
    075        int count = 1;
    076        m_vec[0] = match[0];
    077        t_vec[0] = targets[0];
    078        for (int i = 1; i < match_length; i++) {
    079            final int prev = match[i - 1];
    080            final int gap = match[i] - prev;
    081            for (int j = 1; j < gap; j++) {
    082                m_vec[count] = prev + j;
    083                t_vec[count] = target;
    084                count++;
    085            }
    086            m_vec[count] = match[i];
    087            t_vec[count] = targets[i];
    088            count++;
    089        }
    090        match = new int[count];
    091        targets = new InstructionHandle[count];
    092        System.arraycopy(m_vec, 0, match, 0, count);
    093        System.arraycopy(t_vec, 0, targets, 0, count);
    094    }
    095
    096
    097    /**
    098     * Sort match and targets array with QuickSort.
    099     */
    100    private void sort( final int l, final int r ) {
    101        int i = l;
    102        int j = r;
    103        int h;
    104        final int m = match[(l + r) >>> 1];
    105        InstructionHandle h2;
    106        do {
    107            while (match[i] < m) {
    108                i++;
    109            }
    110            while (m < match[j]) {
    111                j--;
    112            }
    113            if (i <= j) {
    114                h = match[i];
    115                match[i] = match[j];
    116                match[j] = h; // Swap elements
    117                h2 = targets[i];
    118                targets[i] = targets[j];
    119                targets[j] = h2; // Swap instructions, too
    120                i++;
    121                j--;
    122            }
    123        } while (i <= j);
    124        if (l < j) {
    125            sort(l, j);
    126        }
    127        if (i < r) {
    128            sort(i, r);
    129        }
    130    }
    131
    132
    133    /**
    134     * @return match is sorted in ascending order with no gap bigger than max_gap?
    135     */
    136    private boolean matchIsOrdered( final int max_gap ) {
    137        for (int i = 1; i < match_length; i++) {
    138            if (match[i] - match[i - 1] > max_gap) {
    139                return false;
    140            }
    141        }
    142        return true;
    143    }
    144
    145
    146    @Override
    147    public InstructionList getInstructionList() {
    148        return new InstructionList(instruction);
    149    }
    150
    151
    152    public Instruction getInstruction() {
    153        return instruction;
    154    }
    155}