function hexFrom32Bit(num) {
    if (num >= 0) {
        return num.toString(BASE_16);
    }

    // Handle negative numbers
    num = num & 0x7fffffff;
    let tempStr = zeroPad(8, num.toString(BASE_16));
    const topNum = (parseInt(tempStr[0], BASE_16) + 8).toString(BASE_16);
    tempStr = topNum + tempStr.substring(1);
    return tempStr;
}
Convert a 32-bit int to a hexdecimal string
@private
@param  {number} num  Integer to convert
@return {H3Index}     Hexidecimal string