bug#33380: 27.0.50; Emacs hangs in current-time-zone

[Paul Eggert <eggert@cs.ucla.edu>]

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On 11/14/18 10:49 AM, Glenn Morris wrote:
> A smaller example is to evaluate: (calendar-dst-starts 1962)

Thanks for the smaller example. I installed the attached patch into 
master to fix that and am optimistically marking this bug as done. And 
thanks, Sam, for reporting the original problem.


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From 917fe0d0383eabf621f59a7314882423bc12f74a Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@Penguin.CS.UCLA.EDU>
Date: Wed, 14 Nov 2018 11:42:59 -0800
Subject: [PATCH] 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).
---
 lisp/calendar/cal-dst.el | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lisp/calendar/cal-dst.el b/lisp/calendar/cal-dst.el
index 25264bda09..8392e81b16 100644
--- a/lisp/calendar/cal-dst.el
+++ b/lisp/calendar/cal-dst.el
@@ -154,7 +154,7 @@ calendar-next-time-zone-transition
        (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)
-- 
2.19.1