Brainfuck Interpreter

fuck.c

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

#define sblock 8    // Stack block length
#define lblock 4    // Loop-stack block length
#define readln 1024 // Length of input buffer

char* reallocate(char* array, int blocks, int blocksize, int loop, int debug) {
  // Reallocates the input stack if current length is exceeded
  int size = blocks * blocksize;
  char* lstr = (loop) ? "loop " : "";
  if(debug) printf("[\e[1;105m^\e[0m] Increasing %sstack size (to %i)\n", lstr, size);
  char* addr = realloc(array, size);
  if(addr != NULL) return addr;
  exit(EXIT_FAILURE);
}

void brainfuck(char *inp, int debug) {
  char*  stack   = calloc(sblock, sizeof(char));
  int    sblocks = 1;
  char*  sstart  = stack;

  char**  loop    = calloc(lblock, sizeof(char *));
  int     lblocks = 1;
  char**  lstart  = loop;

  if(debug) printf("[\e[1;105m^\e[0m] Stack allocated at    <%p>\n", sstart);
  if(debug) printf("[\e[1;105m^\e[0m] Loop allocated at     <%p>\n", lstart);

  while(*inp != '\0') {
    switch(*inp) {
      case '.' : {
        if(debug) printf("[\e[1;92m.\e[0m] Echoing character at  <%p> (%i) -> ", stack, *stack);
        putchar(*stack);
        if(debug) printf("\n");
        break;
      }

      case ',' : {
        if(debug) printf("[\e[1;92m,\e[0m] Taking Character for  <%p>\n", stack);
        *stack = getchar();
        break;
      }

      case '>' : {
        stack++;
        int diff = (stack - sstart);
        if(diff > (sblocks * sblock)) {
          sstart = reallocate(sstart, ++sblocks, sblock, 0, debug);
          stack = (sstart + diff);
        }
        if(debug) printf("[\e[1;93m>\e[0m] Incrementing pointer  <%p>\n", stack);
        break;
      }

      case '<' : {
        stack--;
        if((stack - sstart) < 0) {
          if(debug) printf("[\e[1;41m<\e[0m] Address <%p> out of range\n", stack);
          exit(EXIT_FAILURE);
        }
        if(debug) printf("[\e[1;93m<\e[0m] Decrementing pointer  <%p>\n", stack);
        break;
      }

      case '+' : {
        *stack = *stack + 1;
        if(debug) printf("[\e[1;96m+\e[0m] Incrementing value at <%p> -> %i\n", stack, *stack);
        break;
      }

      case '-' : {
        *stack = *stack - 1;
        if(debug) printf("[\e[1;96m-\e[0m] Decrementing value at <%p> -> %i\n", stack, *stack);
        break;
      }

      case '[' : {
        if(debug) printf("[\e[1;95m[\e[0m] Loop start -> counter <%p> = %i\n", stack, *stack);
        loop++;
        int diff = (loop - lstart);
        if(diff > (lblocks * lblock)) {
          *lstart = reallocate(*lstart, ++lblocks, lblock, 1, debug);
          loop = (lstart + diff);
        }
        *loop = inp;
        break;
      }

      case ']' : {
        if(debug) printf("[\e[1;95m]\e[0m] Loop end -> ");

        if(*stack <= 0) {
          if(debug) printf("counter   <%p> is zero, continuing with program.\n", stack);
          *loop = 0;
          loop--;
        }
        else {
          if(debug) printf("counter   <%p> is non-zero (%i), looping again.\n", stack, *stack);
          inp = *(loop);
        }
        break;
      }

      case '\n' : {
        // Newlines from STDIN
        break;
      }

      default : {
        if(debug) printf("[\e[1;41m?\e[0m] Unknown symbol \"%c\"\n", *inp);
        exit(EXIT_FAILURE);
      }
    }
    inp++;
  }

  free(sstart);
  free(lstart);
}

char* rdstdin(char* input, int debug) {
  if(debug) printf("[\e[1;41m!\e[0m] Reading from STDIN...\n");
  fgets(input, readln, stdin);
  return input;
}

int main(int argc, char* argv[]) {
  int debug = 0;
  char* input = malloc(readln * sizeof(char));
  if((argc > 1) && (strncmp(argv[1], "--debug", 7) == 0)) {
    debug = 1;
    input = (argc > 2) ? strcpy(input, argv[2]) : rdstdin(input, debug);
  }
  else {
    input = (argc > 1) ? strcpy(input, argv[1]) : rdstdin(input, debug);
  }

  brainfuck(input, debug);
  free(input);
  exit(EXIT_SUCCESS);
}