public long length() {
        //trimTrailingZeros();
        if (wlen == 0) return 0;
        return (((long) wlen - 1) << 6)
                + (64 - Long.numberOfLeadingZeros(word(wlen - 1)));
    }
@return Returns the "logical size" of this {@code BitSet}: the index of
the highest set bit in the {@code BitSet} plus one.
@see java.util.BitSet#length()
indexr-common/src/main/java/io/indexr/util/DirectBitMap.java