Created attachment 1025 [details]
First version of the bit matrix

I suggest to add a fast 2D matrix of bits to Phobos (probably in std_bitmanip):
- It is a common enough data structure, useful for simple implementations of
various games, cellular automata, 2D sets, and more.
- Despite being a simple data structure, it's not obvious, especially if you
want it to be fast. A naive implementation that uses a BitArray is not fast
enough.
- It doesn't need to be too much general. A 3D bit array is in my experience
quite less commonly useful, and the implementation is different enough.


In attach there is an efficient implementation, that I have used it for several
purposes. Some notes:
- It wastes a bit of RAM to be faster.
- I have named it FastBitMatrix because "Fast" helps remember this 2D matrix
wastes some memory to be as fast as possible.
- It uses two little commonly useful functions that in my opinion are better
moved in std.math.
- Currently it allocates memory with a normal dynamic array. With a small
change it's usable with smarter/faster allocators.
- There are ddocs and unittests for all the functions (but the unittests of
FastBitMatrix don't test its contracts).
- I have not tried it on 64 bit systems.
- Optional are a toString/writeTo method, a copy method, postblit, and other
constructors.
- Currently it's just a struct with value semantics.