foo.el

;; This is from simple.el of Bzr-110657. Looks normal? Please take a
;; look at the second if statement. What's the condition, the
;; consequent, and the alternative? Once you thought about that, count
;; parens. (Or paste it over to another buffer and actually let Emacs
;; indent it.)

(defun count-lines (start end)
  "Return number of lines between START and END.
This is usually the number of newlines between them,
but can be one more if START is not equal to END
and the greater of them is not at the start of a line."
  (save-excursion
    (save-restriction
      (narrow-to-region start end)
      (goto-char (point-min))
      (if (eq selective-display t)
	  (save-match-data
	    (let ((done 0))
                     (while (re-search-forward "[\n\C-m]" nil t 40)
                       (setq done (+ 40 done)))
                     (while (re-search-forward "[\n\C-m]" nil t 1)
                       (setq done (+ 1 done)))
                     (goto-char (point-max))
                     (if (and (/= start end)
		       (not (bolp)))
		  (1+ done)
		done)))
	(- (buffer-size) (forward-line (buffer-size)))))))