LocalVariableInstruction 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  import java.io.DataOutputStream;
    20  import java.io.IOException;
    21  import org.apache.bcel.Constants;
    22  import org.apache.bcel.util.ByteSequence;
    23
    24  /***
    25   * Abstract super class for instructions dealing with local variables.
    26   *
    27   * @version $Id: LocalVariableInstruction.java 386056 2006-03-15 11:31:56Z tcurdt $
    28   * @author  <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
    29   */
    30  public abstract class LocalVariableInstruction extends Instruction implements TypedInstruction,
    31          IndexedInstruction {
    32
    33      protected int n = -1; // index of referenced variable
    34      private short c_tag = -1; // compact version, such as ILOAD_0
    35      private short canon_tag = -1; // canonical tag such as ILOAD
    36
    37
    38      private final boolean wide() {
    39          return n > Constants.MAX_BYTE;
    40      }
    41
    42
    43      /***
    44       * Empty constructor needed for the Class.newInstance() statement in
    45       * Instruction.readInstruction(). Not to be used otherwise.
    46       * tag and length are defined in readInstruction and initFromFile, respectively.
    47       */
    48      LocalVariableInstruction(short canon_tag, short c_tag) {
    49          super();
    50          this.canon_tag = canon_tag;
    51          this.c_tag = c_tag;
    52      }
    53
    54
    55      /***
    56       * Empty constructor needed for the Class.newInstance() statement in
    57       * Instruction.readInstruction(). Also used by IINC()!
    58       */
    59      LocalVariableInstruction() {
    60      }
    61
    62
    63      /***
    64       * @param opcode Instruction opcode
    65       * @param c_tag Instruction number for compact version, ALOAD_0, e.g.
    66       * @param n local variable index (unsigned short)
    67       */
    68      protected LocalVariableInstruction(short opcode, short c_tag, int n) {
    69          super(opcode, (short) 2);
    70          this.c_tag = c_tag;
    71          canon_tag = opcode;
    72          setIndex(n);
    73      }
    74
    75
    76      /***
    77       * Dump instruction as byte code to stream out.
    78       * @param out Output stream
    79       */
    80      public void dump( DataOutputStream out ) throws IOException {
    81          if (wide()) {
    82              out.writeByte(Constants.WIDE);
    83          }
    84          out.writeByte(opcode);
    85          if (length > 1) { // Otherwise ILOAD_n, instruction, e.g.
    86              if (wide()) {
    87                  out.writeShort(n);
    88              } else {
    89                  out.writeByte(n);
    90              }
    91          }
    92      }
    93
    94
    95      /***
    96       * Long output format:
    97       *
    98       * &lt;name of opcode&gt; "["&lt;opcode number&gt;"]"
    99       * "("&lt;length of instruction&gt;")" "&lt;"&lt; local variable index&gt;"&gt;"
    100      *
    101      * @param verbose long/short format switch
    102      * @return mnemonic for instruction
    103      */
    104     public String toString( boolean verbose ) {
    105         if (((opcode >= Constants.ILOAD_0) && (opcode <= Constants.ALOAD_3))
    106                 || ((opcode >= Constants.ISTORE_0) && (opcode <= Constants.ASTORE_3))) {
    107             return super.toString(verbose);
    108         } else {
    109             return super.toString(verbose) + " " + n;
    110         }
    111     }
    112
    113
    114     /***
    115      * Read needed data (e.g. index) from file.
    116      * PRE: (ILOAD <= tag <= ALOAD_3) || (ISTORE <= tag <= ASTORE_3)
    117      */
    118     protected void initFromFile( ByteSequence bytes, boolean wide ) throws IOException {
    119         if (wide) {
    120             n = bytes.readUnsignedShort();
    121             length = 4;
    122         } else if (((opcode >= Constants.ILOAD) && (opcode <= Constants.ALOAD))
    123                 || ((opcode >= Constants.ISTORE) && (opcode <= Constants.ASTORE))) {
    124             n = bytes.readUnsignedByte();
    125             length = 2;
    126         } else if (opcode <= Constants.ALOAD_3) { // compact load instruction such as ILOAD_2
    127             n = (opcode - Constants.ILOAD_0) % 4;
    128             length = 1;
    129         } else { // Assert ISTORE_0 <= tag <= ASTORE_3
    130             n = (opcode - Constants.ISTORE_0) % 4;
    131             length = 1;
    132         }
    133     }
    134
    135
    136     /***
    137      * @return local variable index  referred by this instruction.
    138      */
    139     public final int getIndex() {
    140         return n;
    141     }
    142
    143
    144     /***
    145      * Set the local variable index
    146      */
    147     public void setIndex( int n ) {
    148         if ((n < 0) || (n > Constants.MAX_SHORT)) {
    149             throw new ClassGenException("Illegal value: " + n);
    150         }
    151         this.n = n;
    152         if (n >= 0 && n <= 3) { // Use more compact instruction xLOAD_n
    153             opcode = (short) (c_tag + n);
    154             length = 1;
    155         } else {
    156             opcode = canon_tag;
    157             if (wide()) {
    158                 length = 4;
    159             } else {
    160                 length = 2;
    161             }
    162         }
    163     }
    164
    165
    166     /*** @return canonical tag for instruction, e.g., ALOAD for ALOAD_0
    167      */
    168     public short getCanonicalTag() {
    169         return canon_tag;
    170     }
    171
    172
    173     /***
    174      * Returns the type associated with the instruction -
    175      * in case of ALOAD or ASTORE Type.OBJECT is returned.
    176      * This is just a bit incorrect, because ALOAD and ASTORE
    177      * may work on every ReferenceType (including Type.NULL) and
    178      * ASTORE may even work on a ReturnaddressType .
    179      * @return type associated with the instruction
    180      */
    181     public Type getType( ConstantPoolGen cp ) {
    182         switch (canon_tag) {
    183             case Constants.ILOAD:
    184             case Constants.ISTORE:
    185                 return Type.INT;
    186             case Constants.LLOAD:
    187             case Constants.LSTORE:
    188                 return Type.LONG;
    189             case Constants.DLOAD:
    190             case Constants.DSTORE:
    191                 return Type.DOUBLE;
    192             case Constants.FLOAD:
    193             case Constants.FSTORE:
    194                 return Type.FLOAT;
    195             case Constants.ALOAD:
    196             case Constants.ASTORE:
    197                 return Type.OBJECT;
    198             default:
    199                 throw new ClassGenException("Oops: unknown case in switch" + canon_tag);
    200         }
    201     }
    202 }