/*

  * 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.functions;

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

 import org.objectweb.asm.Opcodes;

 import org.objectweb.asm.tree.InsnList;

 import org.objectweb.asm.tree.InsnNode;

 import org.objectweb.asm.tree.MethodInsnNode;

 /** Differentiation transformer for the atanh function invocation instructions.

  * <p>As of java 6, the JVM does not supply an inverse hyperbolic

  * tangent function (see <a

  * href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4919337">bug

  * 4919337</a>), so this generator will not be triggered for java 6 and below.</p>

  */

 public class AtanhTransformer implements MathInvocationTransformer {

     /** {@inheritDoc} */

     public InsnList getReplacementList(final String owner, final MethodDifferentiator methodDifferentiator) {

         // generate differential code

         // ... u0, u1  --> ...  atanh(u0), u1 / (1 - u0 * u0)

         final InsnList list = new InsnList();

         list.add(new InsnNode(Opcodes.DUP2_X2));

         list.add(new InsnNode(Opcodes.POP2));

         list.add(new InsnNode(Opcodes.DUP2_X2));

         list.add(new InsnNode(Opcodes.DUP2));

         list.add(new InsnNode(Opcodes.DMUL));

         list.add(new InsnNode(Opcodes.DCONST_1));

         list.add(new InsnNode(Opcodes.DSUB));

         list.add(new InsnNode(Opcodes.DNEG));

         list.add(new InsnNode(Opcodes.DDIV));

         list.add(new InsnNode(Opcodes.DUP2_X2));

         list.add(new InsnNode(Opcodes.POP2));

         list.add(new MethodInsnNode(Opcodes.INVOKESTATIC, owner, "atanh", D_RETURN_D_DESCRIPTOR));

         list.add(new InsnNode(Opcodes.DUP2_X2));

         list.add(new InsnNode(Opcodes.POP2));

         return list;

     }

 }