12 lines
405 B
Common Lisp
12 lines
405 B
Common Lisp
(defconstant +a+ "ABCDEFGHIJKLMNOPQRSTUVWXYZ")
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(defun strip (s)
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(string-upcase (remove-if-not 'alpha-char-p s)))
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(defun vigenere (txt key &key plain &aux (p (if plain -1 1)))
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(let ((txt (strip txt)) (key (strip key)) (i -1))
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(map 'string
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(lambda (c)
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(setf i (mod (1+ i) (length key)))
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(char +a+ (mod (+ (position c +a+) (* p (position (elt key i) +a+))) 26)))
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txt)))
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