/*

  * 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.apache.commons.nabla.core.DifferentiationException;

 import org.objectweb.asm.Opcodes;

 import org.objectweb.asm.tree.InsnList;

 import org.objectweb.asm.tree.InsnNode;

 import org.objectweb.asm.tree.MethodInsnNode;

 import org.objectweb.asm.tree.VarInsnNode;

 /** Differentiation transformer for the atan2 function invocation instructions.

  */

 public class Atan2Transformer2 implements MathInvocationTransformer {

     /** {@inheritDoc} */

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

         throws DifferentiationException {

         final int tmp1 = methodDifferentiator.getTmp(1);

         final int tmp2 = methodDifferentiator.getTmp(2);

         final int tmp3 = methodDifferentiator.getTmp(3);

         // generate differential code

         // ... y, x0, x1  --> ...  atan2(y, x0), -x1*y/(x0^2+y^2)

         final InsnList list = new InsnList();

         list.add(new VarInsnNode(Opcodes.DSTORE, tmp3)); // => y, x0

         list.add(new VarInsnNode(Opcodes.DSTORE, tmp2)); // => y

         list.add(new VarInsnNode(Opcodes.DSTORE, tmp1)); // =>

         list.add(new VarInsnNode(Opcodes.DLOAD,  tmp1)); // => y

         list.add(new VarInsnNode(Opcodes.DLOAD,  tmp2)); // => y, x0

         list.add(new MethodInsnNode(Opcodes.INVOKESTATIC, owner, "atan2", DD_RETURN_D_DESCRIPTOR)); // => atan2(y,x0)

         list.add(new VarInsnNode(Opcodes.DLOAD,  tmp3)); // => atan2(y,x0), x1

         list.add(new VarInsnNode(Opcodes.DLOAD,  tmp1)); // => atan2(y,x0), x1, y

         list.add(new InsnNode(Opcodes.DMUL));            // => atan2(y,x0), x1*y

         list.add(new InsnNode(Opcodes.DNEG));            // => atan2(y,x0), -x1*y

         list.add(new VarInsnNode(Opcodes.DLOAD,  tmp2)); // => atan2(y,x0), -x1*y, x0

         list.add(new InsnNode(Opcodes.DUP2));            // => atan2(y,x0), -x1*y, x0, x0

         list.add(new InsnNode(Opcodes.DMUL));            // => atan2(y,x0), -x1*y, x0^2

         list.add(new VarInsnNode(Opcodes.DLOAD,  tmp1)); // => atan2(y,x0), -x1*y, x0^2, y

         list.add(new InsnNode(Opcodes.DUP2));            // => atan2(y,x0), -x1*y, x0^2, y, y

         list.add(new InsnNode(Opcodes.DMUL));            // => atan2(y,x0), -x1*y, x0^2, y^2

         list.add(new InsnNode(Opcodes.DADD));            // => atan2(y,x0), -x1*y, x0^2+y^2

         list.add(new InsnNode(Opcodes.DDIV));            // => atan2(y,x0), -x1*y/(x0^2+y^2)

         return list;

     }

 }