valuenumbercache.java

一个查找java程序里bug的程序的源代码,该程序本身也是java写的,对提高java编程水平很有用

/*
 * Bytecode Analysis Framework
 * Copyright (C) 2003,2004 University of Maryland
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package edu.umd.cs.findbugs.ba;

import edu.umd.cs.findbugs.annotations.SuppressWarnings;

import java.util.*;

import org.apache.bcel.generic.InstructionHandle;

/**
 * A cache mapping instructions and input values to the output values they
 * produce.  We must always produce the same output given identical
 * input, or else value number analysis will not terminate.
 *
 * @author David Hovemeyer
 * @see ValueNumberAnalysis
 */
public class ValueNumberCache {
	private static final boolean DEBUG = Boolean.getBoolean("vn.debug");

	/**
	 * An entry in the cache.
	 * It represents an instruction with specific input values.
	 */
	public static class Entry {
		public final InstructionHandle handle;
		public final ValueNumber[] inputValueList;
		private int cachedHashCode;

		@SuppressWarnings("EI2")
		public Entry(InstructionHandle handle, ValueNumber[] inputValueList) {
			this.handle = handle;
			this.inputValueList = inputValueList;
			this.cachedHashCode = 0;
		}

		public boolean equals(Object o) {
			if (!(o instanceof Entry))
				return false;
			Entry other = (Entry) o;
			if (handle.getPosition() != other.handle.getPosition())
				return false;
			ValueNumber[] myList = inputValueList;
			ValueNumber[] otherList = other.inputValueList;
			if (myList.length != otherList.length)
				return false;
			for (int i = 0; i < myList.length; ++i)
				if (!myList[i].equals(otherList[i]))
					return false;
			return true;
		}

		public int hashCode() {
			if (cachedHashCode == 0) {
				int code = handle.getPosition();
				for (int i = 0; i < inputValueList.length; ++i) {
					code *= 101;
					ValueNumber valueNumber = inputValueList[i];
					code += valueNumber.hashCode();
				}
				cachedHashCode = code;
			}
			return cachedHashCode;
		}

		public String toString() {
			StringBuffer buf = new StringBuffer();
			buf.append(handle.toString());
			for (int i = 0; i < inputValueList.length; ++i) {
				buf.append(", ");
				buf.append(inputValueList[i].toString());
			}
			return buf.toString();
		}
	}

	/**
	 * Map of entries to output values.
	 */
	private HashMap<Entry, ValueNumber[]> entryToOutputMap = new HashMap<Entry, ValueNumber[]>();

	/**
	 * Look up cached output values for given entry.
	 *
	 * @param entry the entry
	 * @return the list of output values, or null if there is no matching entry
	 *         in the cache
	 */
	public ValueNumber[] lookupOutputValues(Entry entry) {
		if (DEBUG) System.out.println("VN cache lookup: " + entry);
		ValueNumber[] result = entryToOutputMap.get(entry);
		if (DEBUG) System.out.println("   result ==> " + result);
		return result;
	}

	/**
	 * Add output values for given entry.
	 * Assumes that lookupOutputValues() has determined that the entry
	 * is not in the cache.
	 *
	 * @param entry           the entry
	 * @param outputValueList the list of output values produced
	 *                        by the entry's instruction and input values
	 */
	public void addOutputValues(Entry entry, ValueNumber[] outputValueList) {
		ValueNumber[] old = entryToOutputMap.put(entry, outputValueList);
		if (old != null)
			throw new IllegalStateException("overwriting output values for entry!");
	}

}

// vim:ts=4