I have a C++ ide that allows AVR projects I have played with a little. I also have downloaded ATMEL's IDE but haven't really begun looking into it yet.
Each of them uses the same compiler that the Arduino IDE uses, which does NOT support 64 bit doubles or ints.
In practice I need to measure to approx +/- 4,000,000.0001 meters.
4 million meters at plus/minus one tenth of a millimeter? Get real.