Fix probing for pre-1970 DST

* lisp/calendar/cal-dst.el (calendar-next-time-zone-transition):
Fix recently-introduced rounding bug when probing for DST
transitions before 1970 (Bug#33380).

1 files changed, 1 insertions, 1 deletions

diff --git a/lisp/calendar/cal-dst.el b/lisp/calendar/cal-dst.el
index 25264bda097..8392e81b16f 100644
--- a/lisp/calendar/cal-dst.el
+++ b/lisp/calendar/cal-dst.el
@@ -154,7 +154,7 @@ Return nil if no such transition can be found."
        (while
            ;; Set PROBE to halfway between LO and HI, rounding down.
            ;; If PROBE equals LO, we are done.
-           (not (= lo (setq probe (/ (+ lo hi) 2))))
+           (not (= lo (setq probe (floor (+ lo hi) 2))))
          ;; Set either LO or HI to PROBE, depending on probe results.
          (if (eq (car (current-time-zone probe)) hi-utc-diff)
              (setq hi probe)