Knowing how many layers the layout has

[alex-ong]

In terms of performance, we can do a bit of optimization if we know how many layers there are. This involves:

• adding extern const int NUM_LAYERS to keymap_common.h
• defining const int NUM_LAYERS = ?? in keymap.c

We can then use the num_layers to convert uint32_t's to uint8_t's etc, since 99% of the time people have <8 layers. Another area that could be optimized is when it scans from layer 31 down to layer 0 - it could start at MAX_LAYER instead.

The change is fairly easy to implement, the main issue is whether adding this feature will start other performance related changes that will make the code harder to read.

Thoughts on this kind of feature/and or these kinds of optimizations in general?

[tmk]

Good idea! I don't want users to define NUM_LAYERS if possible. We can use sizeof for this purpose in core/{actionmap, unimap or keymap}.h or somewhere? Not sure that changing integer type of variables is so useful, but we can define type like layer_t instead of uint32_t?

As for optimizastion, we will have to find code section that consumes time first.

[alex-ong]

Not sure that changing integer type of variables is so useful, but we can define type like layer_t instead of uint32_t?

Yes that's what I meant - we use matrix_row_t based on how wide a row is, and therefore I feel like layer_t should also be defined by how many layers there are.

As for determining NUM_LAYERS, sizeof is a neat way of solving the problem.

[alex-ong]

NUM_LAYERS - should it be a #define, a const int or an int?

• int - can be calculated using (sizeof). can't use typedef layer_t based on num_layers
• const int - can only be placed inside the users keymap.c due to keymap not being defined yet. can't use typedef layer_t based on num_layers
• #define - can use typedef layer_t based on num_layers. Requires user to define it, or we write a script to add it to buildflags.

I've hit a brick wall for storing NUM_LAYERS as a const int.

You can't calculate NUM_LAYERS in any file but the file where the layout is defined. This is because calling sizeof in {actionmap,unimap,keymap}.c/h doesn't work because the keymap hasn't been defined yet. https://stackoverflow.com/questions/48413313/c-accessing-incomplete-types-in-linked-files/48413600#48413600

Solutions:

• have user #define the size
• run a shell script that parses the .c file and calculates the size, and then passes that as a buildflag

[tmk]

Ah I see. I coundn't find this problem when I wrote last post. Then I would ditch my idea of auto calc and go simple way, the fomer solution. tmk_core has default value of NUM_LAYERS (in action_layer.h?) and users can change it in their config.h if needed.

I scaned quickly keymaps files in qmk_keyboard and found a keymap with 13 layers! :D https://github.com/qmk/qmk_firmware/blob/master/keyboards/ergodox/keymaps/narze/keymap.c