anchor.diff:                                 :end1 ,block-length-expr
                                  :start2 ciphertext-start)
                         (decrypt-with-mode cipher sub-mode ciphertext plaintext
  -                                         :ciphertext-start ciphertext-start
  -                                         :ciphertext-end ciphertext-end
  -                                         :plaintext-start plaintext-start)
  +                                         ciphertext-start ciphertext-end
  +                                         plaintext-start nil)
                         (setf buffer-index 0)
                         (decf ciphertext-length amount)
                         (incf ciphertext-start amount)
  
positive.code: 
  (defmethod decrypt-with-mode (context (mode stream-mode)
                                ciphertext plaintext
                                &key (ciphertext-start 0) ciphertext-end
                                (plaintext-start 0) handle-final-block)
    (declare (type (simple-array (unsigned-byte 8) (*)) ciphertext plaintext))
    (declare (ignorable handle-final-block mode))
    (let ((length (- (or ciphertext-end (length ciphertext)) ciphertext-start)))
      (when (plusp length)
        (funcall (decrypt-function context) context ciphertext ciphertext-start
                 plaintext plaintext-start length))
  
negative.code:                                                 block-length-expr)
               `(defmethod encrypt-with-mode ((cipher ,cipher-specializer)
                                              (mode ecb-mode) plaintext ciphertext
                                              plaintext-start plaintext-end
                                              ciphertext-start handle-final-block)
                  (declare (type simple-octet-vector plaintext ciphertext))
                  (declare (ignorable handle-final-block))
                  (let ,block-length-binding
                    (loop with offset = plaintext-start
                       with encrypt-function = (encrypt-function cipher)
                       while (<= offset (- plaintext-end ,block-length-expr))
                       do (funcall encrypt-function cipher plaintext offset
  