fibonacci.ytl

unit println([-]u8 string) {
    @print(string);
    @print(@[-]u8 [10,0]);
}

i64 i64_from_string([-]u8 s) {
  i64 ret = 0;
  bool zaporne = false;
  i64 i = 1;
  if ((u8 c = s[0]) == 45) { zaporne = true; c = s[i++] }
  do {
    i64 const = 922337203685477580;  // == floor(2**63 / 10)
    if (ret<=const && (ret!=const || c-48<=(zaporne ? 8 : 7)) && 48<=c<58) {
      ret = 10*ret + (c - 48);
    } else { @exit(1) }
    c = s[i++];
  } while (c != 0);
  return zaporne ?? -ret : ret;
}

[-]u8 string_from_i64(i64 n) {
  [-]u8 temp = "-0123456789012345678";
  if (bool zaporne = (n < 0)) { n *= -1 }
  i64 i = 19;
  do { temp[i--] = @u8(48 + (n % 10)); n /= 10 } while (n > 0);
  i64 delka = (19 - i) + (zaporne ? temp[i--] = 45; 1 : 0);
  [-]u8 preret = @[-]u8(@malloc(8 + delka + 1));
  @[]i64(preret)[] = delka;
  [-]u8 ret = @[-]u8(preret[8]#);
  for (i64 j = 0, i++; j<=delka, j++) { ret[j] = temp[i] }
  return ret;
}

// Computes the n-th Fibonacci number.
i64 fibonacci(i64 n) {
    if (n <= 0) { return 0; }
    if (n == 1) { return 1; }

    i64 f1 = 0;
    i64 f2 = 1;

    for (i64 i = 1, i < n, i++) {
        i64 f3 = f1 + f2;
        f1 = f2;
        f2 = f3;
    }

    return f2;
}

i32 main(i32 argc, [-][-]u8 argv) {
    if (argc != 2) {
        println("expected exactly 1 argument.");
        @print("usage: ");
        @print(argv[0]);
        println(" <number>");
        @exit(1);
    }

    i64 number = i64_from_string(argv[1]);
    i64 result = fibonacci(number);
    [-]u8 result_str = string_from_i64(result);

    @print(argv[1]);
    @print("th Fibonacci number is ");
    println(result_str);

    return 0;
}