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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;

public final class BitUtil {
    private BitUtil() {}

    public static long mask(int from, int to) {
        assert 0 <= from && from <= to && to <= Long.SIZE;
        if (from == to) {
            return 0L;
        }
        if (to == Long.SIZE) {
            return -(1L << from); // = ~((1L << from) - 1L)
        }

        return (1L << to) - 1L & -(1L << from);
    }

    public static long maskTo(int to) {
        assert 0 <= to && to <= Long.SIZE;
        return to == Long.SIZE ? -1L : (1L << to) - 1L;
    }

    public static int nextBit(long store, int index) {
        long shifted = store >>> (index - 1);
        int num = Long.numberOfTrailingZeros(shifted);
        if (num == Long.SIZE) {
            return -1;
        }
        assert num < Long.SIZE - index;
        return num + index + 1;
    }
}