Port message-checksum to bignums

* lisp/gnus/message.el (message--rotate-fixnum-left): New function.
(message-checksum): Use it instead of assuming fixnum-only arithmetic.
This should fix Bug#33083.

1 files changed, 12 insertions, 1 deletions

diff --git a/lisp/gnus/message.el b/lisp/gnus/message.el
index 03f80616d9e..dc15769a4fc 100644
--- a/lisp/gnus/message.el
+++ b/lisp/gnus/message.el
@@ -5400,6 +5400,17 @@ Otherwise, generate and save a value for `canlock-password' first."
              (message "Denied posting -- only quoted text.")
              nil)))))))
 
+(defun message--rotate-fixnum-left (n)
+  "Rotate the fixnum N left by one bit in a fixnum word.
+The result is a fixnum."
+  (logior (if (natnump n) 0 1)
+          (ash (cond ((< (ash most-positive-fixnum -1) n)
+                      (logior n most-negative-fixnum))
+                     ((< n (ash most-negative-fixnum -1))
+                      (logand n most-positive-fixnum))
+                     (n))
+               1)))
+
 (defun message-checksum ()
   "Return a \"checksum\" for the current buffer."
   (let ((sum 0))
@@ -5409,7 +5420,7 @@ Otherwise, generate and save a value for `canlock-password' first."
        (concat "^" (regexp-quote mail-header-separator) "$"))
       (while (not (eobp))
         (when (not (looking-at "[ \t\n]"))
-          (setq sum (logxor (ash sum 1) (if (natnump sum) 0 1)
+          (setq sum (logxor (message--rotate-fixnum-left sum)
                             (char-after))))
         (forward-char 1)))
     sum))