ModbusMaster - Read 64 Bit integer

Question

i'm using ModbusMaster library (Repo) to read from a device some registers.

Many of them are float and i've no problem to read them using the following code:

  //for float conversation
  union
    {
      uint32_t i;
      float f;
    }u;
    uint8_t result = node.readInputRegisters(address, 2); // for 3000xx registers
    Serial.println("Result : " + String(result));// to get error type
    if (result == node.ku8MBSuccess)
    {       
         u.i=(((unsigned long)node.getResponseBuffer(0x01)<<16) | (node.getResponseBuffer(0x00)));// shifting 2nd register to left & stiching with 1st register
    }
    Serial.println("Reading is "+String(u.f));

But i have the energy registers that are 64 Bit unsigned int and i can't figure out how to adapt the above code in order to read them.

Anyone has a solution?