Every vm routine now returns an err_t, which is an enumeration of
possible error states. ERR_OK represents the good state and is 0 so
error checking seems very natural in terms of language `if (err) ...`.
Errors bubble up the runtime, with any callers forced to check if an
error occurred.
This does mean that routines that call other routines cannot provide
an accurate trace of the subcaller (based on the fact that an error is
generated for the current instruction), but this should be a non issue
as no instruction should be complex enough to need proper traces.
Uses the stack and register, respectively, to jump to an absolute
address. The stack based jump pops a word off the stack to perform a
jump, while the register based one uses the operand to figure out
which register to use.
For each cycle, print the cycle and any changes. We track changes on
the stack by remembering the previous stack pointer. For registers, I
remember the previous array of registers and do a byte level compare
of the current registers and the remembered ones.
Produces pretty log messages and an easy way to track execution.
Instead of making routines to handle data in the `ret` register, just
store the result of POP into the last word register.
This means we are no longer using vm_pop_* or POP_ROUTINES for the
vm_execute script on OP_POP: instead we'll just use vm_mov_* which
automatically pops the datum for us, while moving the datum to the
last register.
Registers are now just words, with pushing from and moving to
registers with specified subtypes just pushing those types into the
word registers. That means there are 8 word registers which can act
as 16 half word registers, which themselves can act as 64 byte
registers.
Instead of taking an operand and a register, mov just uses the stack
for the operand. Therefore, there's no need for a register member in
inst_t.
As a result, PUSH_*_REGISTER now uses the operand for the register.
Introduced an enum (opcode_type_t) for the masks and values of each
opcode, which allows defining a single enum which checks an opcode by
a opcode_type_t.
