001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.commons.nabla.algorithmic.forward.arithmetic;
018    
019    import org.apache.commons.nabla.algorithmic.forward.analysis.InstructionsTransformer;
020    import org.apache.commons.nabla.algorithmic.forward.analysis.MethodDifferentiator;
021    import org.apache.commons.nabla.core.DifferentiationException;
022    import org.objectweb.asm.Opcodes;
023    import org.objectweb.asm.tree.AbstractInsnNode;
024    import org.objectweb.asm.tree.InsnList;
025    import org.objectweb.asm.tree.InsnNode;
026    import org.objectweb.asm.tree.VarInsnNode;
027    
028    /** Differentiation transformer for DSUB instructions.
029     * <p>This transformer is used when both arguments of DSUB are
030     * expanded differential pairs. It implements the classical
031     * differentiation rules for subtraction.</p>
032     * @see DSubTransformer1
033     * @see DSubTransformer2
034     */
035    public class DSubTransformer12 implements InstructionsTransformer {
036    
037        // CHECKSTYLE: stop HideUtilityClassConstructor
038        /** Holder for the singleton instance.*/
039        private static class LazyHolder  {
040            /** The singleton instance. */
041            private static final InstructionsTransformer INSTANCE = new DSubTransformer12();
042        }
043        // CHECKSTYLE: resume HideUtilityClassConstructor
044    
045        /** Hidden constructor.
046         */
047        private DSubTransformer12() {
048        }
049    
050        /** Get the singleton instance.
051         * <p>We use here the Initialization on Demand Holder idiom.</p>
052         * @return the singleton instance
053         */
054        public static InstructionsTransformer getInstance() {
055            return LazyHolder.INSTANCE;
056        }
057    
058        /** {@inheritDoc} */
059        public InsnList getReplacement(final AbstractInsnNode insn,
060                                       final MethodDifferentiator methodDifferentiator)
061            throws DifferentiationException {
062    
063            final int tmp = methodDifferentiator.getTmp(1);
064            final InsnList list = new InsnList();
065    
066            // operand stack initial state: a0, a1, b0, b1
067            list.add(new VarInsnNode(Opcodes.DSTORE, tmp)); // => a0, a1, b0
068            list.add(new InsnNode(Opcodes.DUP2_X2));        // => a0, b0, a1, b0
069            list.add(new InsnNode(Opcodes.POP2));           // => a0, b0, a1
070            list.add(new VarInsnNode(Opcodes.DLOAD,  tmp)); // => a0, b0, a1, b1
071            list.add(new InsnNode(Opcodes.DSUB));           // => a0, b0, a1-b1
072            list.add(new VarInsnNode(Opcodes.DSTORE, tmp)); // => a0, b0
073            list.add(new InsnNode(Opcodes.DSUB));           // => a0-b0
074            list.add(new VarInsnNode(Opcodes.DLOAD,  tmp)); // => a0-b0, a1-b1
075    
076            return list;
077    
078        }
079    
080    }