static private String to64(long v,int size){
  final StringBuffer result=new StringBuffer();
  while (--size >= 0) {
    result.append(itoa64.charAt((int)(v & 0x3f)));
    v>>>=6;
  }
  return result.toString();
}

static private String to64 ( long v , int size ) { final StringBuffer result = new StringBuffer ( ) ; while ( -- size >= 0 ) { result . append ( itoa64 . charAt ( ( int ) ( v & 0x3f ) ) ) ; v >>>= 6 ; } return result . toString ( ) ; }
function to return a string from the set : a - za - z0 - 9 . /
