Question

I am having difficulties with my state machine. I use a function that returns the new state based on input parameters oldState and two input parameters.

In this function I have a lot of nested switch cases. I’d rather use a 2×2 transition matrix but have no idea how to use it. I did make a transition table from the state diagram with sates and inputs.

But how exaclty do I use the 2 dim. array transition_table[3][4]?

Answer 1

You stated you currently have something like this:

StateType transition (StateType old, InputType one, InputType two) {
    //... nested switch statements
    return new_state;
}

So, it seems what you need is a 3-dimensional array:

#define MAX_STATES 12
#define MAX_INPUT_VAL 2
StateType transitionTable[MAX_STATES][MAX_INPUT_VAL][MAX_INPUT_VAL] = {
    { { StateA, StateB },
      { StateC, StateD } },
    { { StateE, StateF },
      { StateG, StateH } },
    { { StateI, StateJ },
      { StateK, StateL } },
    //...
};

Then you would transition like this:

new_state = transitionTable[StateIndex(old)][one][two];

So, assuming that StateIndex(StateC) returns 2, then:

old = StateC;
new_state = transitionTable[StateIndex(old)][1][0];
assert(new_state == StateK);

would result in new_state holding StateK.