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.instructions;
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    
027    /** Differentiation transformer for DCMPx instructions.
028     * <p>Each DCMPx instruction is replaced by a sequence that
029     * first remove the differential parts from the top stack cells
030     * followed by the comparison instruction.
031     */
032    public class DcmpTransformer1 implements InstructionsTransformer {
033    
034        // CHECKSTYLE: stop HideUtilityClassConstructor
035        /** Holder for the singleton instance.*/
036        private static class LazyHolder  {
037            /** The singleton instance. */
038            private static final InstructionsTransformer INSTANCE = new DcmpTransformer1();
039        }
040        // CHECKSTYLE: resume HideUtilityClassConstructor
041    
042        /** Hidden constructor.
043         */
044        private DcmpTransformer1() {
045        }
046    
047        /** Get the singleton instance.
048         * <p>We use here the Initialization on Demand Holder idiom.</p>
049         * @return the singleton instance
050         */
051        public static InstructionsTransformer getInstance() {
052            return LazyHolder.INSTANCE;
053        }
054    
055        /** {@inheritDoc} */
056        public InsnList getReplacement(final AbstractInsnNode insn,
057                                       final MethodDifferentiator methodDifferentiator)
058            throws DifferentiationException {
059            final InsnList list = new InsnList();
060            // operand stack initial state: a0, a1, b
061            list.add(new InsnNode(Opcodes.DUP2_X2)); // => a0, b, a1, b
062            list.add(new InsnNode(Opcodes.POP2));    // => a0, b, a1
063            list.add(new InsnNode(Opcodes.POP2));    // => a0, b
064            list.add(methodDifferentiator.clone(insn));
065            return list;
066        }
067    
068    }