Usage: brainf*ck [FILE] brainf*ck -e EXPRESSION

bf.c

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

void
die (const char msg[])
{
  fprintf (stderr, "Error: %s\n", msg);
  exit (1);
}

void
usage ()
{
  fputs ("Usage: brainfuck [FILE]\n", stderr);
  fputs ("       brainfuck -e EXPRESSION\n", stderr);
  exit (0);
}

char *
scan_file (FILE *fp)
{
  int len = 16, i = 0;
  int c;
  char *s = malloc (sizeof (char) * len);

  while (EOF != (c = fgetc (fp)))
    {
      switch (c)
        {
          case '#':
            while ('\n' != c && EOF != c) c = fgetc (fp);
            break;
          case '>': case '<': case '+': case '-':
          case '.': case ',': case '[': case ']':
            if (i == len - 1)
              {
                len *= 2;
                s = realloc (s, sizeof(char) * len);
                if (NULL == s) die ("realloc() failed");
              }
            s[i] = c;
            s[++i] = 0;
            break;
          default:
            break;
        }
    }
  return s;
}

char *
mk_input (int argc, char *argv[])
{
  if (argc > 1)
    {
      if (0 != strcmp (argv[1], "-e"))
        {
          if (argc > 2) usage ();
          FILE *fp = fopen (argv[1], "r");
          if (NULL != fp) return scan_file (fp);
          else usage ();
        }
      else
        {
          if (3 != argc) usage ();
          else return argv[2];
        }
    }
  else return scan_file (stdin);
  return NULL;
}

int
goto_close_bracket (char *s, int i)
{
  int n = 0;
  for (i++; s[i] != 0; i++)
    {
      switch (s[i])
        {
          case '[': n++; break;
          case ']':
            if (0 == n) return i;
            n--; break;
          default : break;
        }
    }
  die ("[: ']' not found"); return 1;
}

int
goto_open_bracket (char *s, int i)
{
  int n = 0;
  for (i--; i >= 0; i--)
    {
      switch (s[i])
        {
          case ']': n++; break;
          case '[':
            if (0 == n) return i;
            n--; break;
          default : break;
        }
    }
  die ("]: '[' not found"); return 1;
}

int
evaluate (char *s)
{
  typedef char byte;
  byte a[30000] = {0}, *z = &a[29999];
  byte *p = a;
  int i;
  for (i = 0; s[i] != 0; i++)
    {
      switch (s[i])
        {
          case '>': (p < z) ? p++ : die(">: buffer overrun"); break;
          case '<': (p > a) ? p-- : die("<: buffer underrun"); break;
          case '+': (*p)++; break;
          case '-': (*p)--; break;
          case '.': putchar(*p); break;
          case ',': *p = getchar(); break;
          case '[': if (*p == 0) i = goto_close_bracket (s, i); break;
          case ']': if (*p != 0) i = goto_open_bracket (s, i); break;
          default : break;
        }
    }
  return 0;
}

int
main (int argc, char *argv[])
{
  char *s = mk_input (argc, argv);
  return evaluate (s);
}