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Datastructures and utility classes for non-negative integers
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/*
 * Copyright (C) 2018 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.set;

import static de.tum.in.naturals.set.NatBitSets.UNKNOWN_LENGTH;
import static de.tum.in.naturals.set.NatBitSets.UNKNOWN_SIZE;

import com.zaxxer.sparsebits.SparseBitSet;
import java.util.BitSet;
import java.util.function.BiPredicate;

public class SparseNatBitSetFactory extends AbstractNatBitSetFactory {
    private static final int SPARSE_THRESHOLD = Long.SIZE * 128;

    private final BiPredicate useSparse;

    SparseNatBitSetFactory() {
        this(SparseNatBitSetFactory::useSparse);
    }

    public SparseNatBitSetFactory(BiPredicate useSparse) {
        this.useSparse = useSparse;
    }

    private static boolean useSparse(int expectedSize, int expectedLength) {
        if (expectedLength == UNKNOWN_LENGTH) {
            if (expectedSize == UNKNOWN_SIZE) {
                return true;
            }
            if (expectedSize > SPARSE_THRESHOLD) {
                return true;
            }
        }
        return expectedLength > SPARSE_THRESHOLD || (expectedSize != UNKNOWN_SIZE && expectedSize > SPARSE_THRESHOLD);
    }

    @Override
    protected BoundedNatBitSet makeBoundedSet(int domainSize, int expectedSize) {
        return useSparse.test(expectedSize, domainSize)
                ? new SparseBoundedNatBitSet(new SparseBitSet(domainSize), domainSize)
                : new SimpleBoundedNatBitSet(new BitSet(domainSize), domainSize);
    }

    @Override
    public NatBitSet set(int expectedSize, int expectedLength) {
        if (useSparse.test(expectedSize, expectedLength)) {
            SparseBitSet backingSet =
                    expectedLength == UNKNOWN_LENGTH ? new SparseBitSet() : new SparseBitSet(expectedLength);
            return new SparseNatBitSet(backingSet);
        }
        return new SimpleNatBitSet(new BitSet(expectedSize));
    }
}