Add bitwise AND, OR and XOR modes to math block

[dominik-korsa]

This PR implements the bitwise AND, bitwise OR and bitwise XOR math block modes from #90.

I've decided not to implement the bitwise NOT operation, as it would require establishing the number of bits in the integer (if Lua used 32-bit or 64-bit integers it would be simple, but it uses doubles instead). The bitwise not operation is equivalent to a bitwise XOR with a number consisting of only binary ones.

The current behaviour for numbers that are not non-negative integers is:

• negative numbers are treated as 0
• non-integers are rounded to the nearest integer (0.1 is treated as 0, 0.5 and 0.9 are treated as 1)

Maybe the behaviour should be different? Should a math.floor operation be used instead of math.round?

[JuneCarya]

Not sure whether this might be relevant, but maybe you might want to have a look into the bit operations library of LuaJIT https://bitop.luajit.org/ and see whether this could be applicable to your implementation.

[dominik-korsa]

Not sure whether this might be relevant, but maybe you might want to have a look into the bit operations library of LuaJIT https://bitop.luajit.org/ and see whether this could be applicable to your implementation.

I can't seem to find the source code for that library (and even if I were able to do so, it's unlikely the C++ implementation would be applicable to my Lua implementation). What's interesting is the page describing the semantics of BitOp. They've decided to only support arithmetic in the range of signed int32 (-31^2 to +31^2-1 inclusive). For Scrap Mechanic where the number type is always a double, integers up to 2^52 could be supported. In BitOp the behaviour for non-integers is implementation-defined and should not be relied upon.

Setting a maximum range would allow to implement the bitwise not operation and bitwise operations on negative integers, but would make the implementation trickier and would require deciding on the behaviour for numbers above 2^52.

[JuneCarya]

If I'm not mistaken the bitwise operation library is exposed to the environment within the table bit.
You should be able to access all bitwise operations with bit.*.

I'm not exactly sure if the SM devs ended up using a different bitwise operations library or the one shipped with LuaJIT.
I suppose you'd have to check what the results of the library's functions are.