question: public int nextClearBit ( int index ) { int i = index > > 6 ; if ( i >= wlen ) return - 1 ; int subIndex = index & 0x3f ; long word = ~ bits . get ( i ) > > subIndex ; if ( word != 0 ) { return ( i << 6 ) + subIndex + Long . numberOfTrailingZeros ( word ) ; } while ( ++ i < wlen ) { word = ~ bits . get ( i ) ; if ( word != 0 ) { return ( i << 6 ) + Long . numberOfTrailingZeros ( word ) ; } } return - 1 ; }
target:  Find the next clear bit in the bit set.