/*

  * 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

  *

  *      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.commons.nabla.automatic.trimming;

 import org.objectweb.asm.tree.AbstractInsnNode;

 import org.objectweb.asm.tree.InsnList;

 /** Base class for code trimmers.

  */

 public abstract class BytecodeTrimmer {

     /** Current instructions window. */

     private AbstractInsnNode[] currentWindow;

     /** Simple constructor.

      * @param lookahead number of lookahead instructions

      */

     protected BytecodeTrimmer(final int lookahead) {

         currentWindow = new AbstractInsnNode[lookahead];

     }

     /** Trim a list of instructions.

      * @param instructions list of instructions to optimize

      */

     public void trim(final InsnList instructions) {

         // set up lookahead instructions

         currentWindow[0] = instructions.get(0);

         for (int i = 1; (i < currentWindow.length) && (currentWindow[i - 1] != null); ++i) {

             currentWindow[i] = currentWindow[i - 1].getNext();

         }

         // trim the whole instructions set using a sliding window

         while (currentWindow[currentWindow.length - 1] != null) {

             // trim current window

             final boolean updated = trimWindow(instructions, currentWindow);

             if (!updated) {

                 // slide the window ourselves one instruction forward

                 for (int i = 1; i < currentWindow.length; ++i) {

                     currentWindow[i - 1] = currentWindow[i];

                 }

                 if (currentWindow[currentWindow.length - 1] != null) {

                     currentWindow[currentWindow.length - 1] = currentWindow[currentWindow.length - 1].getNext();

                 }

             }

         }

     }

     /** Trim the current window of lookahead instructions.

      * @param instructions complete instructions list of instructions to trim

      * @param window current instructions window (belongs to the list)

      * @return true if instructions and window have been updated and are ready

      * for next iteration

      */

     protected abstract boolean trimWindow(InsnList instructions,

                                           AbstractInsnNode[] window);

 }