DefinitelyNullSet.java

/*
 * FindBugs - Find Bugs in Java programs
 * Copyright (C) 2006, 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.npe2;

import java.util.BitSet;

import edu.umd.cs.findbugs.ba.vna.ValueNumber;

/**
 * Set of values that is definitely known to be null.
 * 
 * @author David Hovemeyer
 */
public class DefinitelyNullSet /* extends BitSet */{
    private BitSet contents;

    private int numValueNumbers;

    public DefinitelyNullSet(int numValueNumbers) {
        this.contents = new BitSet();
        this.numValueNumbers = numValueNumbers;
    }

    public NullnessValue getNulllessValue(ValueNumber valueNumber) {
        return getNullnessValue(valueNumber.getNumber());
    }

    private NullnessValue getNullnessValue(int vn) {
        int flags = 0;

        int start = getStartIndex(vn);
        for (int i = 0; i < NullnessValue.FLAGS_MAX; i++) {
            if (contents.get(start + i)) {
                flags |= (1 << i);
            }
        }

        return NullnessValue.fromFlags(flags);
    }

    public void setNullnessValue(ValueNumber valueNumber, NullnessValue nullnessValue) {
        int flags = nullnessValue.getFlags();

        int start = getStartIndex(valueNumber.getNumber());
        for (int i = 0; i < NullnessValue.FLAGS_MAX; i++) {
            contents.set(start + i, (flags & (1 << i)) != 0);
        }
    }

    public void clear() {
        contents.clear();
    }

    public void setTop() {
        contents.clear();
        contents.set(lastUsedBit());
    }

    public boolean isTop() {
        return contents.get(lastUsedBit());
    }

    public void setBottom() {
        contents.clear();
        contents.set(lastUsedBit() + 1);
    }

    public boolean isBottom() {
        return contents.get(lastUsedBit() + 1);
    }

    public boolean isValid() {
        return !(isTop() || isBottom());
    }

    public void makeSameAs(DefinitelyNullSet other) {
        contents.clear();
        contents.or(other.contents);
    }

    public void mergeWith(DefinitelyNullSet other) {
        if (this.isBottom() || other.isTop()) {
            return;
        }

        if (this.isTop() || other.isBottom()) {
            this.makeSameAs(other);
            return;
        }

        // Result is intersection of sets
        this.contents.and(other.contents);
    }

    public BitSet getAssignedNullLocationSet(ValueNumber vn) {
        throw new UnsupportedOperationException();
    }

    public void addAssignedNullLocation(int valueNumber, int locationNumber) {
        // Base class does not maintain this information.
    }

    public void clearAssignNullLocations(int valueNumber) {
        // Base class does not maintain this information.
    }

    private int getStartIndex(int vn) {
        return vn * (1 << NullnessValue.FLAGS_MAX);
    }

    private int lastUsedBit() {
        return numValueNumbers * NullnessValue.FLAGS_MAX;
    }

    private int topBit() {
        return lastUsedBit();
    }

    private int bottomBit() {
        return lastUsedBit() + 1;
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.lang.Object#hashCode()
     */
    @Override
    public int hashCode() {
        return contents.hashCode();
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.lang.Object#equals(java.lang.Object)
     */
    @Override
    public boolean equals(Object obj) {
        if (obj == null || obj.getClass() != this.getClass()) {
            return false;
        }

        DefinitelyNullSet other = (DefinitelyNullSet) obj;
        return this.contents.equals(other.contents);
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.lang.Object#toString()
     */
    @Override
    public String toString() {
        if (isTop()) {
            return "[TOP]";
        } else if (isBottom()) {
            return "[BOTTOM]";
        } else {
            StringBuilder buf = new StringBuilder();
            boolean first = true;

            buf.append("{");

            for (int i = 0; i < numValueNumbers; i++) {
                NullnessValue val = getNullnessValue(i);
                if (val.isDefinitelyNull() || val.isDefinitelyNotNull()) {
                    if (first) {
                        first = false;
                    } else {
                        buf.append(", ");
                    }
                    buf.append(i);
                    buf.append("->");
                    buf.append(val.toString());
                }
            }

            buf.append("}");

            return buf.toString();
        }
    }
}