public ULong subtract(final ULong val) {
        if (this.compareTo(val) < 0) {
            throw new NumberFormatException();
        }

        final long result = value - val.value;
        if (value < 0 && result >= 0) {
            throw new NumberFormatException();
        }

        return valueOf(result);
    }
Create an <code>unsigned long</code>

@throws NumberFormatException If <code>value</code> is not in the range
                              of an <code>unsigned long</code>
tika-parsers/tika-parsers-standard/tika-parsers-standard-modules/tika-parser-microsoft-module/src/main/java/org/apache/tika/parser/microsoft/onenote/fsshttpb/unsigned/ULong.java