I can't imagine any situation where I'd use a u729 instead of a StaticBitSet. For size 729, it would end up backed by a bit_set.Array, not a bit_set.Integer.
I don't program zig, so it's not clear to me if you can use zig's bitsets arithmetically.
Sometimes it's just more clear to work with integers than other representations. Most situations with a state space of N bits have meaningful integer representations, where arithmetic functions on those representations are also meaningful.
For example, CRCs can be written as the remainder from long division of the message by the polynomial. Defining nontrivial cyclic permutations is also much more straightforward as functions on integers than on bitsets.
I was talking about GP's u729, which is 9*9*9, the state space of a sudoku board. Can you come up with a situation where dividing that number by anything is meaningful?
If I had to steel-man the idea, I'm pretty sure the integer-based solution has better codegen with many kinds of sparse, comptime-known masks. I think you're right though, StaticBitSet looks better.
For your specific case, even a simple `[9][9]u16` might perform better (where you make use of nine bits in each u16). For each entry, the nine mask bits would be in the same bit positions, so the compiler won't have to do a bunch of shifts to extract/align the bits. CPUs love consistency. I doubt it's worth the additional codegen complexity to save 70 bytes in your data model.
Sometimes it's just more clear to work with integers than other representations. Most situations with a state space of N bits have meaningful integer representations, where arithmetic functions on those representations are also meaningful.
For example, CRCs can be written as the remainder from long division of the message by the polynomial. Defining nontrivial cyclic permutations is also much more straightforward as functions on integers than on bitsets.