/Brainfuck/interpreter/bf.c

/*
 * A nive brainfuck interpreter.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

char *program(FILE *s)
{
	assert(s);

	char *p;	/* program */
	int ps;		/* available program size */
	int pc;		/* program counter */
	int inc;	/* program size increase amount */
	int c;		/* current character */
	int lb;		/* loop balanced flag */

	p = NULL;
	ps = pc = 0;
	inc = 1000;

	lb = 0;

	while ((c = fgetc(s)) != EOF) {
		if (pc >= ps) {
			ps += inc;
			if ((p = realloc(p, ps)) == NULL) {
				perror("realloc");
				exit(EXIT_FAILURE);
			}
		}

		switch (c) {
			case '>':
			case '<':
			case '+':
			case '-':
			case '.':
			case ',':
				p[pc++] = c;
				break;
			case '[':
				p[pc++] = c;
				lb++;
				break;
			case ']':
				p[pc++] = c;
				lb--;
				break;
			default:
				/* Comments, ignore them. */
				break;
		}
	}

	if (pc >= ps) {
		ps++;
		if ((p = realloc(p, ps)) == NULL) {
			perror("realloc");
			exit(EXIT_FAILURE);
		}
		p[pc] = '\0';
	}

	assert(!lb || !p);
	return p;
}

int main(int argc, char *argv[])
{
	FILE *pf;	/* program file stream */
	char *p;	/* program */
	int pc;		/* program counter */
	char ci;	/* current instruction */
	unsigned char *m;	/* memory */
	int dc;		/* data counter */
	int ml;		/* memory limit */

	if (argc < 2) {
		printf("Usage: %s program\n", argv[0]);
		exit(EXIT_FAILURE);
	}

	if ((pf = fopen(argv[1], "r")) == NULL) {
		perror("fopen");
		exit(EXIT_FAILURE);
	}

	ml = 1000;

	if ((m = malloc(ml)) == NULL) {
		perror("malloc");
		exit(EXIT_FAILURE);
	}

	memset(m, '\0', ml);

	p = program(pf);
	pc = dc = 0;

	while ((ci = p[pc++])) {
		switch (ci) {
			case '>':
				dc++;
				break;
			case '<':
				dc--;
				break;
			case '+':
				m[dc]++;
				break;
			case '-':
				m[dc]--;
				break;
			case '.':
				putchar(m[dc]);
				break;
			case ',':
				m[dc] = getchar();
				break;
			case '[':
				if (m[dc] == 0) {
					for (int i = pc; p[i]; i++) {
						if (p[i] == ']') {
							pc = i + 1;
							break;
						}
					}
				}
				break;
			case ']':
				if (m[dc] != 0) {
					for (int i = pc; i >= 0; i--) {
						if (p[i] == '[') {
							pc = i + 1;
							break;
						}
					}
				}
				break;
			default:
				fprintf(stderr, "Invalid command: %c", ci);
				exit(EXIT_FAILURE);
				break;
		}
	}
}