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A version of the Rhino Javascript engine pulled diretly from the Mozialla repos.
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/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Rhino code, released
 * May 6, 1999.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1997-1999
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Norris Boyd
 *   Roger Lawrence
 *
 * Alternatively, the contents of this file may be used under the terms of
 * the GNU General Public License Version 2 or later (the "GPL"), in which
 * case the provisions of the GPL are applicable instead of those above. If
 * you wish to allow use of your version of this file only under the terms of
 * the GPL and not to allow others to use your version of this file under the
 * MPL, indicate your decision by deleting the provisions above and replacing
 * them with the notice and other provisions required by the GPL. If you do
 * not delete the provisions above, a recipient may use your version of this
 * file under either the MPL or the GPL.
 *
 * ***** END LICENSE BLOCK ***** */



package org.mozilla.javascript.optimizer;

class DataFlowBitSet {

    private int itsBits[];
    private int itsSize;

    DataFlowBitSet(int size)
    {
        itsSize = size;
        itsBits = new int[(size + 31) >> 5];
    }

    void set(int n)
    {
        if (!(0 <= n && n < itsSize)) badIndex(n);
        itsBits[n >> 5] |= 1 << (n & 31);
    }

    boolean test(int n)
    {
        if (!(0 <= n && n < itsSize)) badIndex(n);
        return ((itsBits[n >> 5] & (1 << (n & 31))) != 0);
    }

    void not()
    {
        int bitsLength = itsBits.length;
        for (int i = 0; i < bitsLength; i++)
            itsBits[i] = ~itsBits[i];
    }

    void clear(int n)
    {
        if (!(0 <= n && n < itsSize)) badIndex(n);
        itsBits[n >> 5] &= ~(1 << (n & 31));
    }

    void clear()
    {
        int bitsLength = itsBits.length;
        for (int i = 0; i < bitsLength; i++)
            itsBits[i] = 0;
    }

    void or(DataFlowBitSet b)
    {
        int bitsLength = itsBits.length;
        for (int i = 0; i < bitsLength; i++)
            itsBits[i] |= b.itsBits[i];
    }

    @Override
    public String toString()
    {
        StringBuffer sb = new StringBuffer();
        sb.append("DataFlowBitSet, size = ");
        sb.append(itsSize);
        sb.append('\n');
        int bitsLength = itsBits.length;
        for (int i = 0; i < bitsLength; i++) {
            sb.append(Integer.toHexString(itsBits[i]));
            sb.append(' ');
        }
        return sb.toString();
    }

    boolean df(DataFlowBitSet in, DataFlowBitSet gen, DataFlowBitSet notKill)
    {
        int bitsLength = itsBits.length;
        boolean changed = false;
        for (int i = 0; i < bitsLength; i++) {
            int oldBits = itsBits[i];
            itsBits[i] = (in.itsBits[i] | gen.itsBits[i]) & notKill.itsBits[i];
            changed |= (oldBits != itsBits[i]);
        }
        return changed;
    }

    boolean df2(DataFlowBitSet in, DataFlowBitSet gen, DataFlowBitSet notKill)
    {
        int bitsLength = itsBits.length;
        boolean changed = false;
        for (int i = 0; i < bitsLength; i++) {
            int oldBits = itsBits[i];
            itsBits[i] = (in.itsBits[i] & notKill.itsBits[i]) | gen.itsBits[i];
            changed |= (oldBits != itsBits[i]);
        }
        return changed;
    }

    private void badIndex(int n)
    {
        throw new RuntimeException("DataFlowBitSet bad index " + n);
    }
}