brainfuck.c

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

#define MEM_SIZE 30000
#define BUF_SIZE 2000

void execute(const char prg[]);
int read_file(FILE *f, char buf[], const int bufsize);

int
main(int argc, const char *argv[])
{
    int i;
    FILE *f ;
    char buf[BUF_SIZE];

    if (argc == 1) {
        printf("No input files.\n");
        return 1;
    }

    for (i = 1; i < argc; i++) {
        f = fopen(argv[i], "r");
        if (f == NULL) {
            printf("Invalid input file %d\n", i);
            return 1;
        }
        if (read_file(f, buf, BUF_SIZE)) {
            execute(buf);
        }
        fclose(f);
    }
    return 0;
}

int read_file(FILE *f, char buf[], const int buf_size) {
    int idx = 0;
    char c;

    while (idx < buf_size && (c = getc(f)) != EOF) {
        /* Ignore whitespace */
        if (isspace(c)) {
            continue;
        }
        /* Error on invalid tokens */
        if (c != '+' && c != '-' && c != '>' && c != '<' && c != '.'
            && c != ',' && c != '[' && c != ']')
        {
            printf("Invalid token found in file: '%c'.\n", c);
            return 0;
        }
        buf[idx++] = c;
    }
    buf[idx] = '\0';
    return 1;
}

void
execute(const char prg[])
{

    long t = 0;
    unsigned char mem[MEM_SIZE] = {0};
    int p = MEM_SIZE/2;
    int pc = 0;

    while (prg[pc] != '\0') {
        t++;
        switch (prg[pc]) {
            case '>':
                p++;
                break;
            case '<':
                p--;
                break;
            case '+':
                mem[p]++;
                break;
            case '-':
                mem[p]--;
                break;
            case '.':
                putchar(mem[p]);
                break;
            case ',':
                mem[p] = getchar();
                break;
            case ']':
                if (mem[p] != 0) {
                    while (prg[pc] != '[')
                        pc--;
                }
                break;
            case '[':
                if (mem[p] == 0) {
                    while (prg[pc] != ']')
                        pc++;
                }
                break;
        }

        if (prg[pc] != '\0') {
            pc++;
        }
    }
}