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  1. (defun f (x &optional (length 1))
  2.   (if (integerp x)
  3.       (loop with bits = '()
  4.             for (q r) = (multiple-value-list (floor x 2))
  5.             then (multiple-value-list (floor q 2))
  6.             repeat (max length (1+ (integer-length x)))
  7.             do (push r bits)
  8.             finally (return (if (and (eql x -1) (eql length 1))
  9.                                 (cons 1 bits)
  10.                                 bits)))
  11.       (destructuring-bind (sign-bit . bits) x
  12.         (loop for b in (if (zerop sign-bit)
  13.                            bits
  14.                            (mapcar (lambda (x) (logxor x 1)) bits))
  15.               for i downfrom (1- (length bits))
  16.               sum (* b (expt 2 i)) into n
  17.               finally (return (if (zerop sign-bit) n (- (1+ n))))))))
  18.  
  19. (loop for args in '((10)
  20.                     (10 8)
  21.                     (-8)
  22.                     (-8 8)
  23.                     (-1)
  24.                     nil
  25.                     ((0 1 1 1))
  26.                     ((1 1 1 1))
  27.                     ((1 0 0 0))
  28.                     nil
  29.                     (1)
  30.                     (1 1)
  31.                     (1 2)
  32.                     (-1)
  33.                     (-1 1)
  34.                     (-1 2)
  35.                     nil
  36.                     ((0 1))
  37.                     ((1))
  38.                     ((1 1))
  39.                     nil
  40.                     (0)
  41.                     ((0)))
  42.       do (if args
  43.              (format t "~{~S~^, ~}~10T-> ~S~%" args (apply #'f args))
  44.              (terpri)))
  45.  
Success #stdin #stdout 0.03s 10680KB
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10        -> (0 1 0 1 0)
10, 8     -> (0 0 0 0 1 0 1 0)
-8        -> (1 0 0 0)
-8, 8     -> (1 1 1 1 1 0 0 0)
-1        -> (1 1)

(0 1 1 1) -> 7
(1 1 1 1) -> -1
(1 0 0 0) -> -8

1         -> (0 1)
1, 1      -> (0 1)
1, 2      -> (0 1)
-1        -> (1 1)
-1, 1     -> (1 1)
-1, 2     -> (1 1)

(0 1)     -> 1
(1)       -> -1
(1 1)     -> -1

0         -> (0)
(0)       -> 0
https://ideone.com/Ww1vvV
language:
Common Lisp (clisp 2.49.92)
created:
10 years ago
visibility:
public

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