Truth tables in code? How to structure state machine?
- by HanClinto
I have a (somewhat) large truth table / state machine that I need to implement in my code (embedded C). I anticipate the behavior specification of this state machine to change in the future, and so I'd like to keep this easily modifiable in the future.
My truth table has 4 inputs and 4 outputs. I have it all in an Excel spreadsheet, and if I could just paste that into my code with a little formatting, that would be ideal.
I was thinking I would like to access my truth table like so:
u8 newState[] = decisionTable[input1][input2][input3][input4];
And then I could access the output values with:
setOutputPin( LINE_0, newState[0] );
setOutputPin( LINE_1, newState[1] );
setOutputPin( LINE_2, newState[2] );
setOutputPin( LINE_3, newState[3] );
But in order to get that, it looks like I would have to do a fairly confusing table like so:
static u8 decisionTable[][][][][] =
{{{{ 0, 0, 0, 0 },
{ 0, 0, 0, 0 }},
{{ 0, 0, 0, 0 },
{ 0, 0, 0, 0 }}},
{{{ 0, 0, 1, 1 },
{ 0, 1, 1, 1 }},
{{ 0, 1, 0, 1 },
{ 1, 1, 1, 1 }}}},
{{{{ 0, 1, 0, 1 },
{ 1, 1, 1, 1 }},
{{ 0, 1, 0, 1 },
{ 1, 1, 1, 1 }}},
{{{ 0, 1, 1, 1 },
{ 0, 1, 1, 1 }},
{{ 0, 1, 0, 1 },
{ 1, 1, 1, 1 }}}};
Those nested brackets can be somewhat confusing -- does anyone have a better idea for how I can keep a pretty looking table in my code?
Thanks!
Edit based on HUAGHAGUAH's answer:
Using an amalgamation of everyone's input (thanks -- I wish I could "accept" 3 or 4 of these answers), I think I'm going to try it as a two dimensional array. I'll index into my array using a small bit-shifting macro:
#define SM_INPUTS( in0, in1, in2, in3 ) ((in0 << 0) | (in1 << 1) | (in2 << 2) | (in3 << 3))
And that will let my truth table array look like this:
static u8 decisionTable[][] = {
{ 0, 0, 0, 0 },
{ 0, 0, 0, 0 },
{ 0, 0, 0, 0 },
{ 0, 0, 0, 0 },
{ 0, 0, 1, 1 },
{ 0, 1, 1, 1 },
{ 0, 1, 0, 1 },
{ 1, 1, 1, 1 },
{ 0, 1, 0, 1 },
{ 1, 1, 1, 1 },
{ 0, 1, 0, 1 },
{ 1, 1, 1, 1 },
{ 0, 1, 1, 1 },
{ 0, 1, 1, 1 },
{ 0, 1, 0, 1 },
{ 1, 1, 1, 1 }};
And I can then access my truth table like so:
decisionTable[ SM_INPUTS( line1, line2, line3, line4 ) ]
I'll give that a shot and see how it works out. I'll also be replacing the 0's and 1's with more helpful #defines that express what each state means, along with /**/ comments that explain the inputs for each line of outputs. Thanks for the help, everyone!
