befunge.cc

#include <iostream>
#include <fstream>
#include <string>
#include <stack>
#include <cstring>

struct Program {
  std::stack<int> stack;
  char source[25][81] = {{0}};
  int x = 0, y = 0, dx = 1, dy = 0;
  bool finished = false;

  void move() {
    x = (x + dx + 80) % 80;
    y = (y + dy + 25) % 25;
  }

  int peek() { return stack.empty() ? 0 : stack.top(); }

  int pop() {
    if (stack.empty()) {
      return 0;
    } else {
      int v = stack.top();
      stack.pop();
      return v;
    }
  }

  void step() {
    char c = source[y][x];
    int a, b, v;
    switch (c) {
      case '0':
      case '1':
      case '2':
      case '3':
      case '4':
      case '5':
      case '6':
      case '7':
      case '8':
      case '9':
        stack.push(c - '0');
        break;
      case '+':
        stack.push(pop() + pop());
        break;
      case '-':
        a = pop(); b = pop();
        stack.push(b - a);
        break;
      case '*':
        stack.push(pop() * pop());
        break;
      case '/':
        a = pop(); b = pop();
        stack.push(b / a);
        break;
      case '%':
        a = pop(); b = pop();
        stack.push(b % a);
        break;
      case '!':
        stack.push(!pop());
        break;
      case '`':
        a = pop(); b = pop();
        stack.push(b > a);
        break;
      case '>':
        dx = 1; dy = 0;
        break;
      case '<':
        dx = -1; dy = 0;
        break;
      case 'v':
        dx = 0; dy = 1;
        break;
      case '^':
        dx = 0; dy = -1;
        break;
      case '?':
        v = rand() % 2 == 0 ? -1 : 1;
        if (rand() % 2 == 0) {
          dx = v;
        } else {
          dy = v;
        }
        break;
      case '_':
        if (pop() == 0) {
          dx = 1;
          dy = 0;
        } else {
          dx = -1;
          dy = 0;
        }
        break;
      case '|':
        if (pop() == 0) {
          dx = 0; dy = 1;
        } else {
          dx = 0; dy = -1;
        }
        break;
      case '"':
        while (true) {
          move();
          v = source[y][x];
          if (v == '"') {
            break;
          } else {
            stack.push(v);
          }
        };
        break;
      case ':':
        stack.push(peek());
        break;
      case '\\':
        a = pop(); b = pop();
        stack.push(a);
        stack.push(b);
        break;
      case '$':
        pop();
        break;
      case '.':
        std::cout << pop() << " ";
        break;
      case ',':
        std::cout << ((char)pop());
        break;
      case '#':
        move();
        break;
      case 'p':
        a = pop(); b = pop(); v = pop();
        source[a][b] = v;
        break;
      case 'g':
        a = pop(); b = pop();
        stack.push(source[a][b]);
        break;
      case '&':
        stack.push(std::cin.get() - '0');
        break;
      case '~':
        stack.push(std::cin.get());
        break;
      case '@':
        stack.push(std::cin.get());
        finished = true;
        dx = dy = 0;
        break;
      default:
        break;
    }
    move();
  }

  void run() { while (!finished) step(); }
};

std::istream &operator>>(std::istream &in, Program &program) {
  std::string line;
  for (int y = 0; y < 25; y++) {
    if (std::getline(in, line) == 0) break;
    std::strncpy(program.source[y], line.c_str(), 81);
  }
  return in;
}

int main(int argc, char **argv) {
  Program program;
  std::ifstream in{argv[1], std::ifstream::in};
  in >> program;
  program.run();
  std::cout << std::endl;
  return 0;
}