struct.c is used for the general construction, inspection and deletion
of the virtual machine structure (vm_t). runtime defines the
execution routines, error enum, lookup tables, etc.
Same method as when simplifying OP_POP's implementation: use the
lookup table along with OPCODE_DATA_TYPE abuse. In this case I made a
lookup table called OP_POP for this method to work, but it wasn't difficult.
Very barebones, essentially a simple refactor.
I need to introduce a feature to append to a program as well, but as
it's a flexible structure it will likely have to be functional.
Very easy, they just pop a word then defer to their normal versions.
This is probably the best case where a macro works directly so I
didn't even need to write a function form for them first. One thing
is that then names for the macros are quite bad right now, probably
need renaming.
Pretty simple, required some new types of errors. Obviously there's
space for a macro for the differing instruction implementations, but
these things need to be tested a bit more before I can do that.
As PUSH_REGISTER and MOV have the same signature of taking a word as
input, DUP may as well be part of it.
This leads to a larger discussion about how signatures of functions
matter: I may need to do a cleanup at some point.
Lucky surprise: OP_PLUS follows the same principle rules as the
bitwise operators in that they return the same type as the input.
Therefore I can simply use the same macro to implement it and MULT as
those. Very nice.
Stack based machines generally need "variable space". This may be
quite via a symbol-to-word association a list, a hashmap, or some
other system. Here I decide to go for the simplest: extending the
register system to a dynamic/infinite number of them. This means, in
practice, that we may use a theoretically infinite number of indexed
words, hwords and bytes to act as variable space. This means that the
onus is on those who are targeting this virtual machine to create
their own association system to create syntactic variables: all the
machinery is technically installed within the VM, without the veneer
that causes extra cruft.
A negative number under 2s complement can never be equal to its
positive as the top bit *must* be on. If two numbers are equivalent
bit-by-bit then they are equal for both signed and unsigned numbers.
As it has no dependencies on vm specifically, and it's more necessary
for any vendors who wish to target the virtual machine, it makes more
sense for inst to be a lib module rather than a vm module.
