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