(defstruct (key-chord (:conc-name nil))
  key-code key-string modifiers)

(defun key-chord-hash (kc)
  (let ((factors (list char-code-limit (expt 2 8) 1)))
    (reduce (function +)
            (mapcar (function *)
                    factors
                    (list
                     ;; I assume key-string and modifers are short sequences, so sxhash will be ok.
                     (sxhash (key-string kc))
                     (sxhash (key-code kc))
                     (sxhash (modifiers kc)))))))

(mapcar (function key-chord-hash)
        (list (make-key-chord :key-code 108 :key-string "l" :modifiers '())
              (make-key-chord :key-code 65 :key-string "A" :modifiers '(c))
              (make-key-chord :key-code 65 :key-string "A" :modifiers '(c m))))
;; --> (8482891512445 4956500734673 4956500734851)