Optimized Stack Operations

[deetee]

Power management is essential - so I implemented automatic dimming, display off and finally deep sleep.

Running on a single battery (CR2032) my calculator draws a current of 10 mA (bright display with a lot of "8s"). With a battery capacity of at least 200 mAh it can calculate approximately 20 hours.
After dimming the current falls to 5.5 mA, after deactivating the display 1.1 mA are needed.
In sleep mode it consumes less than 0.25 mA. With a battery capacity of at least 200 mAh it lasts more than a month in sleep mode.

And finally I plan to use 2 (parallel) batteries.