public static int ceilLog(BigInteger a){
  int result=0;
  BigInteger p=ONE;
  while (p.compareTo(a) < 0) {
    result++;
    p=p.shiftLeft(1);
  }
  return result;
}

public static int ceilLog ( BigInteger a ) { int result = 0 ; BigInteger p = ONE ; while ( p . compareTo ( a ) < 0 ) { result ++ ; p = p . shiftLeft ( 1 ) ; } return result ; }
compute the smallest integer that is greater than or equal to the logarithm to the base 2 of the given biginteger .
