/*
    * Copyright  2000-2004 The Apache Software Foundation
    *
    *  Licensed 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
    *
    *      http://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.io.DataOutputStream;
  import java.io.IOException;
  import org.apache.bcel.Constants;
  import org.apache.bcel.util.ByteSequence;
  
  /***
   * Abstract super class for instructions dealing with local variables.
   *
   * @version $Id: LocalVariableInstruction.java 386056 2006-03-15 11:31:56Z tcurdt $
   * @author  <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
   */
  public abstract class LocalVariableInstruction extends Instruction implements TypedInstruction,
          IndexedInstruction {
  
      protected int n = -1; // index of referenced variable
      private short c_tag = -1; // compact version, such as ILOAD_0
      private short canon_tag = -1; // canonical tag such as ILOAD
  
  
      private final boolean wide() {
          return n > Constants.MAX_BYTE;
      }
  
  
      /***
       * Empty constructor needed for the Class.newInstance() statement in
       * Instruction.readInstruction(). Not to be used otherwise.
       * tag and length are defined in readInstruction and initFromFile, respectively.
       */
      LocalVariableInstruction(short canon_tag, short c_tag) {
          super();
          this.canon_tag = canon_tag;
          this.c_tag = c_tag;
      }
  
  
      /***
       * Empty constructor needed for the Class.newInstance() statement in
       * Instruction.readInstruction(). Also used by IINC()!
       */
      LocalVariableInstruction() {
      }
  
  
      /***
       * @param opcode Instruction opcode
       * @param c_tag Instruction number for compact version, ALOAD_0, e.g.
       * @param n local variable index (unsigned short)
       */
      protected LocalVariableInstruction(short opcode, short c_tag, int n) {
          super(opcode, (short) 2);
          this.c_tag = c_tag;
          canon_tag = opcode;
          setIndex(n);
      }
  
  
      /***
       * Dump instruction as byte code to stream out.
       * @param out Output stream
       */
      public void dump( DataOutputStream out ) throws IOException {
          if (wide()) {
              out.writeByte(Constants.WIDE);
          }
          out.writeByte(opcode);
          if (length > 1) { // Otherwise ILOAD_n, instruction, e.g.
              if (wide()) {
                  out.writeShort(n);
              } else {
                  out.writeByte(n);
              }
          }
      }
  
  
      /***
       * Long output format:
       *
       * &lt;name of opcode&gt; "["&lt;opcode number&gt;"]" 
       * "("&lt;length of instruction&gt;")" "&lt;"&lt; local variable index&gt;"&gt;"
      *
      * @param verbose long/short format switch
      * @return mnemonic for instruction
      */
     public String toString( boolean verbose ) {
         if (((opcode >= Constants.ILOAD_0) && (opcode <= Constants.ALOAD_3))
                 || ((opcode >= Constants.ISTORE_0) && (opcode <= Constants.ASTORE_3))) {
             return super.toString(verbose);
         } else {
             return super.toString(verbose) + " " + n;
         }
     }
 
 
     /***
      * Read needed data (e.g. index) from file.
      * PRE: (ILOAD <= tag <= ALOAD_3) || (ISTORE <= tag <= ASTORE_3)
      */
     protected void initFromFile( ByteSequence bytes, boolean wide ) throws IOException {
         if (wide) {
             n = bytes.readUnsignedShort();
             length = 4;
         } else if (((opcode >= Constants.ILOAD) && (opcode <= Constants.ALOAD))
                 || ((opcode >= Constants.ISTORE) && (opcode <= Constants.ASTORE))) {
             n = bytes.readUnsignedByte();
             length = 2;
         } else if (opcode <= Constants.ALOAD_3) { // compact load instruction such as ILOAD_2
             n = (opcode - Constants.ILOAD_0) % 4;
             length = 1;
         } else { // Assert ISTORE_0 <= tag <= ASTORE_3
             n = (opcode - Constants.ISTORE_0) % 4;
             length = 1;
         }
     }
 
 
     /***
      * @return local variable index  referred by this instruction.
      */
     public final int getIndex() {
         return n;
     }
 
 
     /***
      * Set the local variable index
      */
     public void setIndex( int n ) {
         if ((n < 0) || (n > Constants.MAX_SHORT)) {
             throw new ClassGenException("Illegal value: " + n);
         }
         this.n = n;
         if (n >= 0 && n <= 3) { // Use more compact instruction xLOAD_n
             opcode = (short) (c_tag + n);
             length = 1;
         } else {
             opcode = canon_tag;
             if (wide()) {
                 length = 4;
             } else {
                 length = 2;
             }
         }
     }
 
 
     /*** @return canonical tag for instruction, e.g., ALOAD for ALOAD_0
      */
     public short getCanonicalTag() {
         return canon_tag;
     }
 
 
     /***
      * Returns the type associated with the instruction - 
      * in case of ALOAD or ASTORE Type.OBJECT is returned.
      * This is just a bit incorrect, because ALOAD and ASTORE
      * may work on every ReferenceType (including Type.NULL) and
      * ASTORE may even work on a ReturnaddressType .
      * @return type associated with the instruction
      */
     public Type getType( ConstantPoolGen cp ) {
         switch (canon_tag) {
             case Constants.ILOAD:
             case Constants.ISTORE:
                 return Type.INT;
             case Constants.LLOAD:
             case Constants.LSTORE:
                 return Type.LONG;
             case Constants.DLOAD:
             case Constants.DSTORE:
                 return Type.DOUBLE;
             case Constants.FLOAD:
             case Constants.FSTORE:
                 return Type.FLOAT;
             case Constants.ALOAD:
             case Constants.ASTORE:
                 return Type.OBJECT;
             default:
                 throw new ClassGenException("Oops: unknown case in switch" + canon_tag);
         }
     }
 }