public static long xorCount(DirectBitMap a, DirectBitMap b) {
        long tot = BitUtil.pop_xor(a.bitsBase, a.bitsAddr, b.bitsBase, b.bitsAddr, 0, Math.min(a.wlen, b.wlen));
        if (a.wlen < b.wlen) {
            tot += BitUtil.pop_array(b.bitsBase, b.bitsAddr, a.wlen, b.wlen - a.wlen);
        } else if (a.wlen > b.wlen) {
            tot += BitUtil.pop_array(a.bitsBase, a.bitsAddr, b.wlen, a.wlen - b.wlen);
        }
        return tot;
    }
@param a The first set
@param b The second set
@return Returns the popcount or cardinality of the exclusive-or of the two sets. Neither
set is modified.
indexr-common/src/main/java/io/indexr/util/DirectBitMap.java