https://learn.sparkfun.com/tutorials/da ... in-arduino
However I do not know if this applies to the esp8266 port which compiles without error with uint64_t variables. To confirm what is happening I need to be able to print 64 bit integers. Others have also had the need to print 64 bit integers and have written library code for the AVR:
http://forum.arduino.cc/index.php?topic=143584.0
I have ported the code over to esp8266 and have it to the point where it will compile but have not yet confirmed that it works.