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/*
 * JBoss, Home of Professional Open Source
 * Copyright 2008, Red Hat, Inc., and individual contributors
 * by the @authors tag. See the copyright.txt in the distribution for a
 * full listing of individual contributors.
 *
 * Licensed 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.jboss.weld.util.bytecode;

import javassist.bytecode.Bytecode;

/**
 * Utilities for writiting conditional statements in bytecode
 *
 * @author Stuart Douglas
 */
public class JumpUtils {
    /**
     * After writing the instruction that requires a branch offset (e.g. GOTO )
     * to the {@link Bytecode} call this method. This will write two zero bytes
     * to the stream. When you have reached the position in the bytecode that you
     * want the jump to end at call {@link JumpMarker#mark()}, this will update
     * the branch offset to point to the next bytecode instruction that is added
     *
     * @return The JumpMarker that is used to set the conditionals end point
     */
    public static JumpMarker addJumpInstruction(Bytecode code) {
        return new JumpMarkerImpl(code);
    }

    private static class JumpMarkerImpl implements JumpMarker {
        private final Bytecode code;
        private int position;

        public JumpMarkerImpl(Bytecode code) {
            this.code = code;
            this.position = code.currentPc() - 1;
            code.addIndex(0);
        }

        public void mark() {
            code.write16bit(position + 1, code.currentPc() - position);
        }
    }
}




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