buffer-space-mode.el

(defclass bsm-mapid-table ()
  ((%by-key :reader by-key
             :initarg :by-key
             :initform nil)
   (%by-value :reader by-value
              :initarg :by-value
              :initform nil)))

(defun bsm-make-bsm-mapid-table (by-key-test by-value-test)
  (bsm-mapid-table :by-key (make-hash-table :test by-key-test)
                   :by-value (make-hash-table :test by-value-test)))

(defun bsm-put-mapid-table (key value mitbl)
  (puthash key value (by-key mitbl))
  (puthash value value (by-value mitbl)))

(defun bsm-get-mapid-table (thing mitbl)
  (let ((item (gethash thing (by-key mitbl))))
    (if item
        item
      (let ((item (gethash thing (by-value mitbl))))
        (if item
            item
          nil)))))

(defun bsm-remhash-mapid-table (thing mitbl)
  (remhash thing (by-key mitbl))
  (remhash thing (by-value mitbl)))