Improving FIX mode

[c3d]

In DB48X, I decided to implement the FIX mode a bit differently than traditional HP calculators do. The idea is to avoid displaying non-significant zeroes. The difference is that DB48X switches to engineering mode as soon as it cannot display non-zero significant digits, whereas HP calculators traditionally will display leading zeroes in that case.

Here is a comparison in FIX 4 for 1/2, 1/20, 1/200, 1/2000, ... and 1/3, 1/30, ...

The HP48 displays
0.5000, 0.0500, 0.0050, 0.0005, 0.0001, 5.0000E-6,
0.3333, 0.0333, 0.0033, 0.0003, 3.3333E-5, 3.3333E-6

DB48X displays
0.5000, 0.0500, 0.0050, 0.0005, 5.0000E-5, 5.0000E-6
3.3333E-1, 3.3333E-2, 3.3333E-3, 3.3333E-4, 3.3333E-5, 3.3333E-6

I personally prefer that, so I want to be able to keep my preferred display. However, someone already contacted me to report that this was unexpected. So I am considering adding an option.

I see two ways to recover the HP behaviour:

- One option would be to add yet another display mode (DB48X already has FIX, SCI, ENG and SIG, the latter being inspired by C47 / WP34). It could be called ADFIX (all-digits FIX).

- Another option, which I prefer, would be to have another setting indicating how many non-significant leading zeroes you allow. If 4 or more in FIX4, you would get the HP behaviour. A value of 9 would get you the HP behaviour for all values of FIX.

What do you think?

If at all possible, please copy your thoughts here: https://github.com/c3d/DB48X-on-DM42/issues/412.