anchor.diff:       (dolist (input-filepath input-filepaths)
          (with-open-file (in input-filepath :element-type 'octet)
            (write-bigendian-uint4 (file-length in) out)))
  -
  -     (dolist (input-filepath input-filepaths)
  -       (with-open-file (in input-filepath :element-type 'octet)
  -         (let ((buf (make-array (file-length in) :element-type 'octet)))
  -           (read-sequence buf in)
  -           (write-sequence buf out)))))))
  +     
  +     (let ((buffer (make-array +BUFFER_SIZE+ :element-type 'octet)))
  +       (dolist (input-filepath input-filepaths)
  +         (with-open-file (in input-filepath :element-type 'octet)
  +           (copy-stream in out buffer)))))))
   
   ;;;;;;;;;;;;;;;;;;
   ;;; build function
  
positive.code: (declaim #.*fastest*
           (inline set-base set-chck set-opts))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;; da (abbreviation of "double array")
  (defstruct da
  
negative.code: (defun temp-path (base ext)
    (format nil "~A.~A.~A" base ext (gentemp)))
  
  (defun copy-stream (from to buffer)
    (let ((read (read-sequence buffer from)))
      (write-sequence buffer to :end read)
      (when (= read (length buffer))
        (copy-stream from to buffer))))
  
  (defun concat-files (output-filepath &rest input-filepaths)
    (muffle
     (with-open-file (out output-filepath :element-type 'octet
  