anchor.diff:                         ifd-entry
                        (write-int-16 stream tag)
                        (write-int-16 stream field-type)
  -                     (let* ((field-count (if (atom values)
  -                                             1
  -                                             (length values)))
  +                     (let* ((field-count (if (sequencep values)
  +                                             (length values)
  +                                             1))
                               (field-size
                                (* (field-length field-type) field-count)))
                          (write-int-32 stream field-count)
  
positive.code:     (write-int-16 stream (aref array i))))
  
  (defun write-int-16-sequence (stream values)
    (if (atom values)
        (write-int-16 stream values)
        (write-int-16-array stream (vectorize values))))
  
  (defun read-int-32 (stream)
    (let ((bytes (read-bytes stream 4)))
  
negative.code:   (defconstant +planar-configuration-tag+ 284)
    (defconstant +resolution-unit-tag+ 296)
    (defconstant +predictor-tag+ 317)
  
    (defconstant +photometric-interpretation-white-is-zero+ 0)
    (defconstant +photometric-interpretation-black-is-zero+ 1)
    (defconstant +photometric-interpretation-rgb+ 2)
  
    (defconstant +horizontal-differencing+ 2)
  
    (defconstant +packbits-compression+ #x8005)
  