I have written a simple brainfuck interpreter in MATLAB script language. It is fed random bf programs to execute (as part of a genetic algorithm project). The problem I face is, the program turns out to have an infinite loop in a sizeable number of cases, and hence the GA gets stuck at the point.
So, I need a mechanism to detect infinite loops and avoid executing that code in bf.
One obvious (trivial) case is when I have
++++ Put 4 in 1st cell (1)
>+++ Put 3 in (2)
<[ While( (1) is non zero)
-- Decrease (1) by 2
>[ While( (2) is non zero)
- Decrement (2)
<+ Increment (1)
(2) would be 0 at this point
+++ Increase (2) by 3 making (2) = 3
<] (1) was decreased by 2 and then increased by 3, so net effect is increment
Looping through the bfprogram,
If(current character is '[')
Find the corresponding ']'
Store the code between the two brackets in, say, 'subprog'
Save the value of the current cell in oldval
Call bfexec recursively with subprog
Save the value of the current cell in newval
If(newval >= oldval)
Raise an 'infinite loop' error and exit
/* Do other character's processings */
When I used linear genetic programming, I just used an upper bound for the number of instructions a single program was allowed to do in its lifetime. I think that this is sensible in two ways: I cannot really solve the halting problem anyway, and programs that take too long to compute are not worthy of getting more time anyway.