BitSet.java

/*
 * Copyright (C) 2012, Google Inc. and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.internal.storage.file;

import java.util.Arrays;

import com.googlecode.javaewah.EWAHCompressedBitmap;

/**
 * A random access BitSet to supports efficient conversions to
 * EWAHCompressedBitmap.
 */
final class BitSet {

    private long[] words;

    BitSet(int initialCapacity) {
        words = new long[block(initialCapacity) + 1];
    }

    final void clear() {
        Arrays.fill(words, 0);
    }

    final void set(int position) {
        int block = block(position);
        if (block >= words.length) {
            long[] buf = new long[2 * block(position)];
            System.arraycopy(words, 0, buf, 0, words.length);
            words = buf;
        }
        words[block] |= mask(position);
    }

    final void clear(int position) {
        int block = block(position);
        if (block < words.length)
            words[block] &= ~mask(position);
    }

    final boolean get(int position) {
        int block = block(position);
        return block < words.length && (words[block] & mask(position)) != 0;
    }

    final EWAHCompressedBitmap toEWAHCompressedBitmap() {
        EWAHCompressedBitmap compressed = new EWAHCompressedBitmap(
                words.length);
        int runningEmptyWords = 0;
        long lastNonEmptyWord = 0;
        for (long word : words) {
            if (word == 0) {
                runningEmptyWords++;
                continue;
            }

            if (lastNonEmptyWord != 0)
                compressed.addWord(lastNonEmptyWord);

            if (runningEmptyWords > 0) {
                compressed.addStreamOfEmptyWords(false, runningEmptyWords);
                runningEmptyWords = 0;
            }

            lastNonEmptyWord = word;
        }
        int bitsThatMatter = 64 - Long.numberOfLeadingZeros(lastNonEmptyWord);
        if (bitsThatMatter > 0)
            compressed.addWord(lastNonEmptyWord, bitsThatMatter);
        return compressed;
    }

    private static final int block(int position) {
        return position >> 6;
    }

    private static final long mask(int position) {
        return 1L << position;
    }
}