Arithmetic range error

[Colin Baxter <m43cap@yandex.com>]

I originally posted an Arithmetic range error using org-publish to
gmane.emacs.orgmode. My original post is
[[gnus:gmane.emacs.orgmode#87ef8jwzs5.fsf@yandex.com][here]].

It was suggested that I also report it to emacs-dev. The error occurs
using org-mode from git and seems to effect emacs-26.1 but not
emacs-27.0.50. With a very inelegant ECM below, I can reproduce the
arithmetic range error. I have tested the ECM on machines running Debian
3.16.0-7-686-pae and Debian 4.9.0-8-686-pae, with the same results.

------ Begin ECM -------------

1. emacs -Q <RET>

2. We need a directory for testing. This ECM uses ~/temp.

3. In the scratch buffer, evaluate the following:

#+begin_src emacs-lisp
(add-to-list 'load-path (expand-file-name "~/path/to/git/org-mode/lisp"))
#+end_src

#+begin_src emacs-lisp
(setq org-publish-project-alist
      '(("org"
         :base-directory "~/temp/"
         :publishing-directory "~/temp"
         :publishing-function org-html-publish-to-html)))
#+end_src

4. Create file ~/temp/test.org.

5. Enter some text (e.g. This is a test) in test.org and save file.

6. M-x org-publish-current-file <RET>.

7. A satisfactory ~/temp/test.html is produced.

8. emacs-26.1 gives 'org-publish-cache-ctime-of-src: Arithmetic range
error: "floor", 1549541220.7500212'

9. emacs-27.0.50 gives no arithmetic range error.

10. Also no errors are produced if emacs-26.1 and emacs-27.0.50 use only
their generic org-modes, namely 'release_9.1.9-65-g5e4542'.

------ End ECM -------------

The issue is apparently triggered by a backport of Emacs's 662bee7d7,
specifically:

* lisp/ox-publish.el (org-publish-cache-ctime-of-src):
Prefer float-time to doing time arithmetic by hand.
[...]
@@ -1364,8 +1366,7 @@ (defun org-publish-cache-ctime-of-src (file)
 	       (expand-file-name (or (file-symlink-p file) file)
 				 (file-name-directory file)))))
     (if (not attr) (error "No such file: \"%s\"" file)
-      (+ (ash (car (nth 5 attr)) 16)
-	 (cadr (nth 5 attr))))))
+      (floor (float-time (file-attribute-modification-time attr))))))


It would appear that the code is sound, but if the above commit is
reversed then the error disappears.

-- 
Colin Baxter
m43cap@yandex.com