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Datastructures and utility classes for non-negative integers

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/*
 * Copyright (C) 2017 Tobias Meggendorfer
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */

package de.tum.in.naturals.bitset;

import it.unimi.dsi.fastutil.ints.IntIterator;
import java.util.BitSet;
import java.util.Iterator;
import java.util.NoSuchElementException;

final class PowerBitSetIterator implements Iterator {
    private final BitSet baseSet;
    private final BitSet iteration;
    private final int baseCardinality;
    private int numSetBits = -1;

    PowerBitSetIterator(BitSet baseSet) {
        this.baseSet = baseSet;
        this.baseCardinality = baseSet.cardinality();
        this.iteration = new BitSet(baseSet.length());
    }

    @Override
    public boolean hasNext() {
        return numSetBits < baseCardinality;
    }

    @Override
    public BitSet next() {
        if (numSetBits == -1) {
            numSetBits = 0;
            return iteration;
        }

        if (numSetBits == baseCardinality) {
            throw new NoSuchElementException("No next element");
        }

        IntIterator iterator = BitSets.iterator(baseSet);
        while (iterator.hasNext()) {
            int index = iterator.nextInt();
            if (iteration.get(index)) {
                iteration.clear(index);
                numSetBits -= 1;
            } else {
                iteration.set(index);
                numSetBits += 1;
                break;
            }
        }

        return iteration;
    }
}