/* simple brainfuck interpreter */
/* 20 April 2006 */
/* Daniel B. Cristofani */
/* http://www.brainfuck.org/ */

#include <stdio.h>
#include <stdlib.h>
#define ARRAYSIZE 16777216
#define MAXCODESIZE 65536

//For simplicity, we'll use statically allocated arrays with matching indices.
int stack[MAXCODESIZE], stackp; //to store locations of still-unmatched '['s.
char code[MAXCODESIZE];
int codep, codelength;          //copy of the program we'll read into memory.
short int array[ARRAYSIZE];
int memp;                       //the memory used by the brainfuck program.
int targets[MAXCODESIZE];       //to save matching '[' for each ']' and vice versa.
int c;
FILE *prog;

int main(int argc, char **argv)
{
	if (argc > 2)
		fprintf(stderr, "Too many arguments.\n"), exit(1);
	if (argc < 2) {
		prog = stdin;
	} else {
		if (!(prog = fopen(argv[1], "r")))
			fprintf(stderr, "Can't open the file %s.\n", argv[1]), exit(1);
	}
	codelength = fread(code, 1, MAXCODESIZE, prog);
	if (argc >= 2)
		fclose(prog);
	for (codep = 0; codep < codelength; codep++) {
		if (code[codep] == '[')
			stack[stackp++] = codep;        //put each '[' on the stack
		if (code[codep] == ']') {       //If we meet a ']',
			if (stackp == 0) {      //and there is no '[' left on the stack, it's an error.
				fprintf(stderr,
				        "Unmatched ']' at byte %d.",
				        codep), exit(1);
			} else {
				--stackp;       //if there is one, we take the matching '[' from the stack top,
				targets[codep] = stack[stackp]; //save it as the match for the current ']',
				targets[stack[stackp]] = codep; //and save the current ']' as the match for it.
			}
		}
	}
	if (stackp > 0) {       //Any unmatched '['s still left on the stack are an error too.
		fprintf(stderr, "Unmatched '[' at byte %d.",
		        stack[--stackp]), exit(1);
	}
	for (codep = 0; codep < codelength; codep++) {  //Everything is okay; we start executing the program.
		switch (code[codep]) {
		case '+':
			array[memp]++;
			break;
		case '-':
			array[memp]--;
			break;
		case '<':
			memp--;
			break;
		case '>':
			memp++;
			break;
		case ',':
			if ((c = getchar()) != EOF)
				array[memp] = c == '\n' ? 10 : c;
			break;
		case '.':
			putchar(array[memp] == 10 ? '\n' : array[memp]);
			fflush(stdout);
			break;
		case '[':
			if (!array[memp])
				codep = targets[codep];
			break;
		case ']':
			if (array[memp])
				codep = targets[codep];
			break;
		}
	}
	exit(0);
}