#-sbcl (error "This only works using SBCL")
(declaim (optimize (speed 3)
                   (debug 0)
                   (safety 0)))

(defmacro gen-arccot (sign opposite)
  `(,(intern (format nil "~a~a" 'arccot sign)) (x-rest n x-elevate product)
      "Arccotangent calculator, uses"
      (declare (type integer x-elevate x-rest n product))
      (let ((term (floor x-elevate n)))
        (if (zerop term)
            product
          (,(intern (format nil "~a~a" 'arccot opposite)) x-rest (+ n 2)
             (floor x-elevate x-rest)
             (,(intern (format nil "~a" sign)) product term ))))))


(defun pidigits (x-digits)
  "Calculate x-digits of pi using Machin's formula"
  (labels ((gen-arccot + -)
           (gen-arccot - +))
    (let* ((limit (expt 10 (+ 10 x-digits)))
           (first-thread (sb-thread:make-thread
                          (lambda () (* 44 (the bignum (arccot+ 3249 1 (the bignum (floor limit 57)) 1))))))
           (second-thread (sb-thread:make-thread
                           (lambda () (* 7 (the bignum (arccot+ 57121 1 (the bignum (floor limit 239)) 1))))))
           (third-thread (sb-thread:make-thread
                          (lambda () (* -12 (the bignum (arccot+ 465124 1 (the bignum (floor limit 682)) 1))))))
           (fourth-thread (sb-thread:make-thread
                           (lambda () (* 24 (the bignum (arccot+ 167521249 1 (the bignum (floor limit 12943)) 1)))))))
      (declare (type bignum limit))
      (sb-thread:thread-yield)
      (format nil "3.~a" (the bignum (rem
                                      (the bignum (floor
                                                   (the bignum (* 4
                                                                  (the bignum (+
                                                                               (the bignum (sb-thread:join-thread fourth-thread))
                                                                               (the bignum (sb-thread:join-thread third-thread))
                                                                               (the bignum (sb-thread:join-thread second-thread))
                                                                               (the bignum (sb-thread:join-thread first-thread))))))
                                                   10000000000))
                                      (/ limit 10000000000)))))))


(if (not (cadr *posix-argv*))
  (format t "Error: you should pass an argument~%")
  (let ((n (parse-integer (cadr *posix-argv*))))
    (if (not (typep n 'integer))
      (print "The argument should be a integer~%")
      (print (pidigits n)))))