anchor.diff:    (let* ((mask (coerce (reduce (lambda (prev next) (+ prev (ash 1 (car next))))
                                  elements
                                  :initial-value 0)
  -                       `(unsigned-byte ,(read-mask-length factory))))
  +                       '(unsigned-byte 64)))
            (size (logcount mask)))
       (make-instance 'fixed-lookuptable
                      :mask mask
  
positive.code: 
  (defun apply-mask-to-index (index mask)
    (declare (type index index)
             (type (unsigned-byte 32) mask))
    (assert (< index 32))
    (logcount (ldb (byte index 0) mask)))
  
  
negative.code:   ((%replacer
      :type vector-replacer
      :initarg :replacer
      :reader read-replacer)))
  
  
  @export
  