def _idToStr(self, x):
        """
        Convert VCD id in int to string
        """
        if x < 0:
            sign = -1
        elif x == 0:
            return self._idChars[0]
        else:
            sign = 1
        x *= sign
        digits = []
        while x:
            digits.append(self._idChars[x % self._idCharsCnt])
            x //= self._idCharsCnt
        if sign < 0:
            digits.append('-')
        digits.reverse()

        return ''.join(digits)
Convert VCD id in int to string