Improve precision of float numbers

[deetee]

@Claudio: Thanks for guiding me to the source of newRPL. Very impressive and for me a good reference for details - but I agree it doesn't fit in my small MCU.

@Jonathan: Thanks for this hint. Impressive, comprehensive and easy readable code. DEC64 is similar to what I intended. I expected to get rid of bit shifting and & operations by separating mantissa and exponent in different (struct) variables. And I agree with you - to implement entering and displaying of numbers is not easy. First shots cost me approx. 5k ... I worry if I find room for "real" calculator stuff.

Finally I'm close to give up and do it with the intrinsic double format - even if it's 7-decimal-precision only.

Regards
deetee