code: private static String getMantissa(final String str, final int stopPos) {
          final char firstChar = str.charAt(0);
          final boolean hasSign = firstChar == '-' || firstChar == '+';
  
          return hasSign ? str.substring(1, stopPos) : str.substring(0, stopPos);
      }
docs: <p>Utility method for {@link #createNumber(java.lang.String)}.</p>
  
  <p>Returns mantissa of the given number.</p>
  
  @param str the string representation of the number
  @param stopPos the position of the exponent or decimal point
  @return mantissa of the given number