A Brainfuck Interpreter in C

Brainfuck is an esoteric programming language noted for its extreme minimalism. The language consists of only eight simple commands and an instruction pointer. It is designed to challenge and amuse programmers, and was not made to be suitable for practical use. It was created in 1993 by Urban Müller - Wikipedia

In short brainfuck has eight commands or instructions:

+ : Increments the value at the current cell by one.
- : Decrements the value at the current cell by one.
> : Moves the data pointer to the next cell (cell on the right).
< : Moves the data pointer to the previous cell (cell on the left).
. : Prints the ASCII value at the current cell (i.e. 65 = 'A').
, : Reads a single input character into the current cell.
[ : If the value at the current cell is zero, skips to the corresponding ] .
    Otherwise, move to the next instruction.
] : If the value at the current cell is zero, move to the next instruction.
    Otherwise, move backwards in the instructions to the corresponding [ . 

Here is a basic brainfuck interpreter in C that takes brainfuck code, works on it and produces the intended output. The implementation uses a recursive approach (why ? because brainfuck) and a stack for interpreting the brainfuck code. The examples include a multiplication code, addition of a series of numbers and some ASCII printing. The code is compiled and tested on  Visual C++ 2010 Express.There are several other ways to interpret brainfuck code, this is just one of those...

Next i will try to see the possiblity of implementing this on an FPGA. 

	/*
	Brainfuck Interpreter Code.
	http://en.wikipedia.org/wiki/Brainfuck
	A recursive, stack based implementation in C
	Scaling Options:
	MAX_CELLS - Increase cell count depending on brainfuck program
	MAX_STACK_SZ - Increase stack size.
	Author : Rishi F.
	Copyright (c) 2014 Rishi F.
	Permission is hereby granted, free of charge, to any person obtaining a copy
	of this software and associated documentation files (the "Software"), to deal
	in the Software without restriction, including without limitation the rights
	to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	copies of the Software, and to permit persons to whom the Software is
	furnished to do so, subject to the following conditions:
	The above copyright notice and this permission notice shall be included in
	all copies or substantial portions of the Software.
	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
	THE SOFTWARE.
	*/
	#include<stdio.h>
	#include<string.h>
	#include<stdlib.h>
	#define MAX_CELLS 512
	int cells[MAX_CELLS] = { 0, };
	int *ptr = cells;
	int debug_index = 0;
	#define MAX_STACK_SZ 1024
	static char *stack[MAX_STACK_SZ] = { (char *)0, };
	static int stack_ptr = 0;
	#define push(p) (stack[stack_ptr++] = p)
	#define pop() (stack[--stack_ptr])
	#define empty() (stack_ptr == 0)
	#define full() (stack_ptr == MAX_STACK_SZ)
	#define ERR_SUCCESS 0
	#define ERR_FAILURE 1
	int codeCheck(char *code)
	{
	// Check for invalid characters
	char *save = code;
	while (*code != '\0')
	{
	switch (*code)
	{
	case '>':
	case '<':
	case '.':
	case ',':
	case '+':
	case '-':
	case '[':
	case ']':
	case ' ': // ignore whitespaces, tabs
	case '\t':
	break;
	default:
	printf("Error in BF Code at index: %d\n", ((int)code - (int)save));
	return ERR_FAILURE;
	}
	code++;
	}
	// Check [] parentheses balancing
	code = save;
	while (*code != '\0')
	{
	if (full()){ exit(1); }
	if (*code == '['){ push(code); }
	if (*code == ']'){
	if (empty()){
	printf("Unbalanced [ ]\n");
	return ERR_FAILURE;
	}
	pop();
	}
	code++;
	}
	if (!empty()){
	printf("Unbalanced [ ]\n");
	return ERR_FAILURE;
	}
	return ERR_SUCCESS;
	}
	void reset_cells()
	{
	// clear array
	memset(cells, 0, MAX_CELLS);
	debug_index = 0;
	ptr = cells;
	printf("\n");
	}
	char *brainfuck(char *s)
	{
	char *save = s;
	while (*s != '\0') {
	switch (*s)
	{
	case '+':
	++*ptr; s++;
	break;
	case '-':
	--*ptr; s++;
	break;
	case '>':
	++ptr; ++debug_index; s++;
	break;
	case '<':
	--ptr; --debug_index; s++;
	break;
	case '.':
	putchar(*ptr); s++;
	break;
	case ',':
	*ptr = getchar(); s++;
	break;
	case '[':
	if (full()){ exit(1); } //crude error handling
	if (*ptr == 0){
	push(s);
	while (!empty())
	{
	if (*++s == '['){ push(s); }
	if (*++s == ']'){ pop(); }
	}
	s++;
	}
	else {
	push(s);
	s = brainfuck(s + 1);
	s++;
	}
	break;
	case ']':
	if (*ptr == 0)
	{
	if (empty()) { exit(1); }
	pop();
	return s;
	}
	else
	{
	s = save;
	}
	break;
	default:
	s++;
	break;
	}
	}
	return s;
	}
	int main()
	{
	char *bfcode_multiply = "[ > [ >+ >+ << -] >> [- << + >>] <<< -] >>";
	char *bfcode_sum = "[>>>>> + <<<<< -] > [>>>> + <<<< -] > [>>> + <<< -] > [>> + << -] > [> + < -]";
	char *bfcode_while = "> - [ < ++ [ - ] +++";
	char *bfcode_invalid = "> -[<] ++{ ] ++ + ";
	char *bfcode_parenthesis = "> - [ < ] ++ [ - ] ] +++";
	char *bfcode_bffed = "> -[<] ++[] +` + ] -";
	char *bfcode_author[] = {
	"++++++++ [ > ++++++++++ < - ] > ++ . >",
	"+++++++ [ > ++++++++++ < - ] > +++ . >",
	"++++++++ [ > ++++++++++ < - ] > +++ . >",
	"+++++++ [ > ++++++++++ < - ] > ++ . >",
	"+++++++ [ > ++++++++++ < - ] > +++ . >"
	};
	// You can add code here to verify input BF code string.
	// Error check for any characters other than the ones specified by BF
	// Check for balanced square brackets
	cells[0] = 15;
	cells[1] = 2;
	// Multiply numbers stored in cell[0] and cell[1]
	// Result in cell[2]
	brainfuck(bfcode_multiply);
	reset_cells();
	cells[0] = 3;
	cells[1] = 5;
	cells[2] = 1;
	cells[3] = 9;
	cells[4] = 6;
	// Add numbers in cell[0 ... 4]
	// Store result in cell[5]
	brainfuck(bfcode_sum);
	reset_cells();
	// ASCII display
	brainfuck(bfcode_author[0]);
	brainfuck(bfcode_author[1]);
	brainfuck(bfcode_author[2]);
	brainfuck(bfcode_author[3]);
	brainfuck(bfcode_author[4]);
	reset_cells();
	// Invalidity tests
	codeCheck(bfcode_invalid);
	codeCheck(bfcode_parenthesis);
	codeCheck(bfcode_bffed);
	reset_cells();
	cells[1] = 1;
	if (!codeCheck(bfcode_while)) {
	brainfuck(bfcode_while);
	}
	return 0;
	}

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