SWITCH xref

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    1   /*
    2    * Copyright  2000-2004 The Apache Software Foundation
    3    *
    4    *  Licensed under the Apache License, Version 2.0 (the "License");
    5    *  you may not use this file except in compliance with the License.
    6    *  You may obtain a copy of the License at
    7    *
    8    *      http://www.apache.org/licenses/LICENSE-2.0
    9    *
    10   *  Unless required by applicable law or agreed to in writing, software
    11   *  distributed under the License is distributed on an "AS IS" BASIS,
    12   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13   *  See the License for the specific language governing permissions and
    14   *  limitations under the License.
    15   *
    16   */
    17  package org.apache.bcel.generic;
    18
    19  /***
    20   * SWITCH - Branch depending on int value, generates either LOOKUPSWITCH or
    21   * TABLESWITCH instruction, depending on whether the match values (int[]) can be
    22   * sorted with no gaps between the numbers.
    23   *
    24   * @version $Id: SWITCH.java 386056 2006-03-15 11:31:56Z tcurdt $
    25   * @author  <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
    26   */
    27  public final class SWITCH implements CompoundInstruction {
    28
    29      private int[] match;
    30      private InstructionHandle[] targets;
    31      private Select instruction;
    32      private int match_length;
    33
    34
    35      /***
    36       * Template for switch() constructs. If the match array can be
    37       * sorted in ascending order with gaps no larger than max_gap
    38       * between the numbers, a TABLESWITCH instruction is generated, and
    39       * a LOOKUPSWITCH otherwise. The former may be more efficient, but
    40       * needs more space.
    41       *
    42       * Note, that the key array always will be sorted, though we leave
    43       * the original arrays unaltered.
    44       *
    45       * @param match array of match values (case 2: ... case 7: ..., etc.)
    46       * @param targets the instructions to be branched to for each case
    47       * @param target the default target
    48       * @param max_gap maximum gap that may between case branches
    49       */
    50      public SWITCH(int[] match, InstructionHandle[] targets, InstructionHandle target, int max_gap) {
    51          this.match = (int[]) match.clone();
    52          this.targets = (InstructionHandle[]) targets.clone();
    53          if ((match_length = match.length) < 2) {
    54              instruction = new TABLESWITCH(match, targets, target);
    55          } else {
    56              sort(0, match_length - 1);
    57              if (matchIsOrdered(max_gap)) {
    58                  fillup(max_gap, target);
    59                  instruction = new TABLESWITCH(this.match, this.targets, target);
    60              } else {
    61                  instruction = new LOOKUPSWITCH(this.match, this.targets, target);
    62              }
    63          }
    64      }
    65
    66
    67      public SWITCH(int[] match, InstructionHandle[] targets, InstructionHandle target) {
    68          this(match, targets, target, 1);
    69      }
    70
    71
    72      private final void fillup( int max_gap, InstructionHandle target ) {
    73          int max_size = match_length + match_length * max_gap;
    74          int[] m_vec = new int[max_size];
    75          InstructionHandle[] t_vec = new InstructionHandle[max_size];
    76          int count = 1;
    77          m_vec[0] = match[0];
    78          t_vec[0] = targets[0];
    79          for (int i = 1; i < match_length; i++) {
    80              int prev = match[i - 1];
    81              int gap = match[i] - prev;
    82              for (int j = 1; j < gap; j++) {
    83                  m_vec[count] = prev + j;
    84                  t_vec[count] = target;
    85                  count++;
    86              }
    87              m_vec[count] = match[i];
    88              t_vec[count] = targets[i];
    89              count++;
    90          }
    91          match = new int[count];
    92          targets = new InstructionHandle[count];
    93          System.arraycopy(m_vec, 0, match, 0, count);
    94          System.arraycopy(t_vec, 0, targets, 0, count);
    95      }
    96
    97
    98      /***
    99       * Sort match and targets array with QuickSort.
    100      */
    101     private final void sort( int l, int r ) {
    102         int i = l, j = r;
    103         int h, m = match[(l + r) / 2];
    104         InstructionHandle h2;
    105         do {
    106             while (match[i] < m) {
    107                 i++;
    108             }
    109             while (m < match[j]) {
    110                 j--;
    111             }
    112             if (i <= j) {
    113                 h = match[i];
    114                 match[i] = match[j];
    115                 match[j] = h; // Swap elements
    116                 h2 = targets[i];
    117                 targets[i] = targets[j];
    118                 targets[j] = h2; // Swap instructions, too
    119                 i++;
    120                 j--;
    121             }
    122         } while (i <= j);
    123         if (l < j) {
    124             sort(l, j);
    125         }
    126         if (i < r) {
    127             sort(i, r);
    128         }
    129     }
    130
    131
    132     /***
    133      * @return match is sorted in ascending order with no gap bigger than max_gap?
    134      */
    135     private final boolean matchIsOrdered( int max_gap ) {
    136         for (int i = 1; i < match_length; i++) {
    137             if (match[i] - match[i - 1] > max_gap) {
    138                 return false;
    139             }
    140         }
    141         return true;
    142     }
    143
    144
    145     public final InstructionList getInstructionList() {
    146         return new InstructionList(instruction);
    147     }
    148
    149
    150     public final Instruction getInstruction() {
    151         return instruction;
    152     }
    153 }