code: func (iter *Iterator) ReadBigFloat() (ret *big.Float) {
  	str := iter.readNumberAsString()
  	if iter.Error != nil && iter.Error != io.EOF {
  		return nil
  	}
  	prec := 64
  	if len(str) > prec {
  		prec = len(str)
  	}
  	val, _, err := big.ParseFloat(str, 10, uint(prec), big.ToZero)
  	if err != nil {
  		iter.Error = err
  		return nil
  	}
  	return val
  }
docs: // ReadBigFloat read big.Float