fine-third/fine-roaringbitmap/src/com/fr/third/bitmap/roaringbitmap/BitSetUtil.java

package com.fr.third.bitmap.roaringbitmap;


import java.util.Arrays;
import java.util.BitSet;


/***
 *
 * This class provides convenience functions to manipulate BitSet and RoaringBitmap objects.
 *
 */
public class BitSetUtil {
    // todo: add a method to convert a RoaringBitmap to a BitSet using BitSet.valueOf

    // a block consists has a maximum of 1024 words, each representing 64 bits,
    // thus representing at maximum 65536 bits
    static final private int BLOCK_LENGTH = BitmapContainer.MAX_CAPACITY / Long.SIZE; //
    // 64-bit
    // word

    private static ArrayContainer arrayContainerOf(final int from, final int to,
                                                   final int cardinality, final long[] words) {
        // precondition: cardinality is max 4096
        final short[] content = new short[cardinality];
        int index = 0;

        for (int i = from, socket = 0; i < to; ++i, socket += Long.SIZE) {
            long word = words[i];
            while (word != 0) {
                long t = word & -word;
                content[index++] = (short) (socket + Long.bitCount(t - 1));
                word ^= t;
            }
        }
        return new ArrayContainer(content);
    }

    /**
     * Generate a RoaringBitmap out of a long[], each long using little-endian representation of its
     * bits
     *
     * @param words array of longs (will not be modified)
     * @return roaring bitmap
     * @see BitSet#toLongArray() for an equivalent
     */
    public static RoaringBitmap bitmapOf(final long[] words) {
        // split long[] into blocks.
        // each block becomes a single container, if any bit is set
        final RoaringBitmap ans = new RoaringBitmap();
        int containerIndex = 0;
        for (int from = 0; from < words.length; from += BLOCK_LENGTH) {
            final int to = Math.min(from + BLOCK_LENGTH, words.length);
            final int blockCardinality = cardinality(from, to, words);
            if (blockCardinality > 0) {
                ans.highLowContainer.insertNewKeyValueAt(containerIndex++, Util.highbits(from * Long.SIZE),
                        BitSetUtil.containerOf(from, to, blockCardinality, words));
            }
        }
        return ans;
    }

    private static int cardinality(final int from, final int to, final long[] words) {
        int sum = 0;
        for (int i = from; i < to; i++) {
            sum += Long.bitCount(words[i]);
        }
        return sum;
    }


    private static Container containerOf(final int from, final int to, final int blockCardinality,
                                         final long[] words) {
        // find the best container available
        if (blockCardinality <= ArrayContainer.DEFAULT_MAX_SIZE) {
            // containers with DEFAULT_MAX_SIZE or less integers should be
            // ArrayContainers
            return arrayContainerOf(from, to, blockCardinality, words);
        } else {
            // otherwise use bitmap container
            return new BitmapContainer(Arrays.copyOfRange(words, from, from + BLOCK_LENGTH),
                    blockCardinality);
        }
    }


    /**
     * Compares a RoaringBitmap and a BitSet. They are equal if and only if they contain the same set
     * of integers.
     *
     * @param bitset first object to be compared
     * @param bitmap second object to be compared
     * @return whether they are equals
     */
    public static boolean equals(final BitSet bitset, final RoaringBitmap bitmap) {
        if (bitset.cardinality() != bitmap.getCardinality()) {
            return false;
        }
        final IntIterator it = bitmap.getIntIterator();
        while (it.hasNext()) {
            int val = it.next();
            if (!bitset.get(val)) {
                return false;
            }
        }
        return true;
    }
}