/*

  * 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.instructions;

 import org.apache.commons.nabla.automatic.analysis.InstructionsTransformer;

 import org.apache.commons.nabla.automatic.analysis.MethodDifferentiator;

 import org.apache.commons.nabla.core.DifferentiationException;

 import org.objectweb.asm.Opcodes;

 import org.objectweb.asm.tree.AbstractInsnNode;

 import org.objectweb.asm.tree.InsnList;

 import org.objectweb.asm.tree.InsnNode;

 /** Differentiation transformer for DCMPx instructions.

  * <p>Each DCMPx instruction is replaced by a sequence that

  * first remove the differential parts from the top stack cells

  * followed by the comparison instruction.

  */

 public class DcmpTransformer1 implements InstructionsTransformer {

     /** Holder for the singleton instance.*/

     private static class LazyHolder  {

         /** The singleton instance. */

         private static final InstructionsTransformer INSTANCE = new DcmpTransformer1();

     }

     /** Hidden constructor.

      */

     private DcmpTransformer1() {

     }

     /** Get the singleton instance.

      * <p>We use here the Initialization on Demand Holder idiom.</p>

      * @return the singleton instance

      */

     public static InstructionsTransformer getInstance() {

         return LazyHolder.INSTANCE;

     }

     /** {@inheritDoc} */

     public InsnList getReplacement(final AbstractInsnNode insn,

                                    final MethodDifferentiator methodDifferentiator)

         throws DifferentiationException {

         final InsnList list = new InsnList();

         // operand stack initial state: a0, a1, b

         list.add(new InsnNode(Opcodes.DUP2_X2)); // => a0, b, a1, b

         list.add(new InsnNode(Opcodes.POP2));    // => a0, b, a1

         list.add(new InsnNode(Opcodes.POP2));    // => a0, b

         list.add(methodDifferentiator.clone(insn));

         return list;

     }

 }