public BitVector(BitVector s){
  bits=new int[s.bits.length];
  this.nbits=s.nbits;
  System.arraycopy(s.bits,0,this.bits,0,s.bits.length);
}

public BitVector ( BitVector s ) { bits = new int [ s . bits . length ] ; this . nbits = s . nbits ; System . arraycopy ( s . bits , 0 , this . bits , 0 , s . bits . length ) ; }
creates a copy of a bit string
