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(calendar-time-zone-daylight-rules): Scan through the
next few years until at most one rule remains; if none remain, then
just use the first candidate rule; it's wrong in general, but it's
right for at least one year. This is a better heuristic in case the
underlying time zone implementation has bugs (which is all too
common). If possible, don't convert back and forth between gregorian
and absolute; this speeds things up noticeably. This uses the new
calendar-nth-named-absday function.
(calendar-current-time-zone): Some locales start DST at a different
time of day than they end; allow for this by yielding both times. The
performance speedups in calendar.el are great enough that we now no
longer need the "Checking time zone data..." message. If
current-time-zone yields nil, don't bother with
calendar-next-time-zone-transition. Use clearer names for local vars.
(calendar-time-zone, calendar-daylight-time-offset,
calendar-{standard,daylight}-time-zone-name,
calendar-daylight-savings-{starts,ends}): Default to US Eastern rules
for information that is not available.
(calendar-daylight-savings-{starts,ends}-time): New vars, replacing
calendar-daylight-savings-switchover-time, to support locales that
start DST at a different time of day than they end.
(calendar-absolute-from-time):
Fix typo by interchanging floor and mod.
This commit is contained in:
Paul Eggert
parent
04d5d338d2
commit
6bc457fea5
@ -62,9 +62,9 @@ absolute date ABS-DATE is the equivalent moment to X."
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;; Overflow is a terrible thing!
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(cons (+ calendar-system-time-basis
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;; floor((2^16 h +l) / (60*60*24))
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(* 512 (mod h 675)) (floor u 675))
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(* 512 (floor h 675)) (floor u 675))
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;; (2^16 h +l) % (60*60*24)
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(+ (* (mod u 675) 128) (floor l 128)))))
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(+ (* (mod u 675) 128) (mod l 128)))))
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(defun calendar-time-from-absolute (abs-date s)
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"Time of absolute date ABS-DATE, S seconds after midnight.
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@ -169,32 +169,44 @@ The result has the proper form for calendar-daylight-savings-starts'."
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(- (calendar-absolute-from-hebrew
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(list 7 1 (+ year 3761))) 3))))))))
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(prevday-sec (- -1 utc-diff)) ;; last sec of previous local day
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last-surviving-rule
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(i 1))
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;; Scan through the next few years; take the rule that explains them best.
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(while (and candidate-rules (cdr candidate-rules) (<= i 28))
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(let ((year (+ y i))
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new-rules)
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(while candidate-rules
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(let* ((rule (car candidate-rules))
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(date (calendar-absolute-from-gregorian (eval rule))))
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(or (equal (current-time-zone
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(calendar-time-from-absolute date prevday-sec))
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(current-time-zone
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(calendar-time-from-absolute (1+ date) prevday-sec)))
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(progn
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(setq new-rules (cons rule new-rules))
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(setq last-surviving-rule rule))))
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(setq candidate-rules (cdr candidate-rules)))
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(setq candidate-rules (nreverse new-rules)))
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(setq i (1+ i)))
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last-surviving-rule))
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(year (1+ y)))
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;; Scan through the next few years until only one rule remains.
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(while
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(let ((rules candidate-rules)
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new-rules)
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(while
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(let*
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((rule (car rules))
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(date
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;; The following is much faster than
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;; (calendar-absolute-from-gregorian (eval rule)).
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(cond ((eq (car rule) 'calendar-nth-named-day)
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(eval (cons 'calendar-nth-named-absday (cdr rule))))
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((eq (car rule) 'calendar-gregorian-from-absolute)
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(eval (car (cdr rule))))
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(t (let ((g (eval rule)))
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(calendar-absolute-from-gregorian g))))))
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(or (equal
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(current-time-zone
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(calendar-time-from-absolute date prevday-sec))
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(current-time-zone
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(calendar-time-from-absolute (1+ date) prevday-sec)))
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(setq new-rules (cons rule new-rules)))
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(setq rules (cdr rules))))
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;; If no rules remain, just use the first candidate rule;
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;; it's wrong in general, but it's right for at least one year.
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(setq candidate-rules (if new-rules (nreverse new-rules)
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(list (car candidate-rules))))
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(setq year (1+ year))
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(cdr candidate-rules)))
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(car candidate-rules)))
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(defun calendar-current-time-zone ()
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"Return UTC difference, dst offset, names and rules for current time zone.
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Returns (UTC-DIFF DST-OFFSET STD-ZONE DST-ZONE DST-STARTS DST-ENDS DST-SWITCH),
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based on a heuristic probing of what the system knows:
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Returns (UTC-DIFF DST-OFFSET STD-ZONE DST-ZONE DST-STARTS DST-ENDS
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DST-STARTS-TIME DST-ENDS-TIME), based on a heuristic probing of what the
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system knows:
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UTC-DIFF is an integer specifying the number of minutes difference between
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standard time in the current time zone and Coordinated Universal Time
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@ -205,87 +217,88 @@ STD-ZONE is a string giving the name of the time zone when no seasonal time
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DST-ZONE is a string giving the name of the time zone when there is a seasonal
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time adjustment in effect.
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DST-STARTS and DST-ENDS are sexps in the variable `year' giving the daylight
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savings time start rules, in the form expected by
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savings time start and end rules, in the form expected by
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`calendar-daylight-savings-starts'.
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DST-SWITCH is an integer giving the number of minutes after midnight that
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daylight savings time starts or ends.
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DST-STARTS-TIME and DST-ENDS-TIME are integers giving the number of minutes
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after midnight that daylight savings time starts and ends.
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If the local area does not use a seasonal time adjustment, DST-OFFSET and
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DST-SWITCH are 0, STD-ZONE and DST-ZONE are equal, and DST-STARTS and DST-ENDS
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are nil.
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If the local area does not use a seasonal time adjustment, STD-ZONE and
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DST-ZONE are equal, and all the DST-* integer variables are 0.
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Some operating systems cannot provide all this information to Emacs; in this
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case, `calendar-current-time-zone' returns a list containing nil for the data
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it can't find."
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(or
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calendar-current-time-zone-cache
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(progn
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(message "Checking time zone data...")
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(setq
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calendar-current-time-zone-cache
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(let* ((now (current-time))
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(now-zone (current-time-zone now))
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(now-utc-diff (car now-zone))
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(now-name (car (cdr now-zone)))
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(next (calendar-next-time-zone-transition now)))
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(if (null next)
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(list (and now-utc-diff (/ now-utc-diff 60))
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0 now-name now-name nil nil 0)
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(let* ((next-zone (current-time-zone next))
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(next-utc-diff (car next-zone))
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(next-name (car (cdr next-zone)))
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(next-absdate-seconds
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(calendar-absolute-from-time next now-utc-diff))
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(next-transitions
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(calendar-time-zone-daylight-rules
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(car next-absdate-seconds) now-utc-diff))
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(nextnext (calendar-next-time-zone-transition next))
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(now-transitions
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(calendar-time-zone-daylight-rules
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(car (calendar-absolute-from-time nextnext next-utc-diff))
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next-utc-diff))
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(now-is-std (< now-utc-diff next-utc-diff)))
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(list (/ (min now-utc-diff next-utc-diff) 60)
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(/ (abs (- now-utc-diff next-utc-diff)) 60)
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(if now-is-std now-name next-name)
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(if now-is-std next-name now-name)
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(if now-is-std next-transitions now-transitions)
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(if now-is-std now-transitions next-transitions)
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(/ (cdr next-absdate-seconds) 60))))))
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(message "Checking time zone data...done")))
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calendar-current-time-zone-cache)
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(setq
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calendar-current-time-zone-cache
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(let* ((t0 (current-time))
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(t0-zone (current-time-zone t0))
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(t0-utc-diff (car t0-zone))
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(t0-name (car (cdr t0-zone))))
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(if (not t0-utc-diff)
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;; Little or no time zone information is available.
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(list nil nil t0-name t0-name nil nil nil nil)
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(let* ((t1 (calendar-next-time-zone-transition t0))
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(t2 (and t1 (calendar-next-time-zone-transition t1))))
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(if (not t2)
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;; This locale does not have daylight savings time.
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(list (/ t0-utc-diff 60) 0 t0-name t0-name nil nil 0 0)
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;; Use heuristics to find daylight savings parameters.
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(let* ((t1-zone (current-time-zone t1))
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(t1-utc-diff (car t1-zone))
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(t1-name (car (cdr t1-zone)))
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(t1-date-sec (calendar-absolute-from-time t1 t0-utc-diff))
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(t2-date-sec (calendar-absolute-from-time t2 t1-utc-diff))
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(t1-rules (calendar-time-zone-daylight-rules
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(car t1-date-sec) t0-utc-diff))
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(t2-rules (calendar-time-zone-daylight-rules
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(car t2-date-sec) t1-utc-diff))
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(t1-time (/ (cdr t1-date-sec) 60))
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(t2-time (/ (cdr t2-date-sec) 60)))
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(cons
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(/ (min t0-utc-diff t1-utc-diff) 60)
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(cons
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(/ (abs (- t0-utc-diff t1-utc-diff)) 60)
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(if (< t0-utc-diff t1-utc-diff)
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(list t0-name t1-name t1-rules t2-rules t2-time t1-time)
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(list t1-name t0-name t2-rules t1-rules t1-time t2-time)
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)))))))))))
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;;; The following six defvars relating to daylight savings time should NOT be
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;;; marked to go into loaddefs.el where they would be evaluated when Emacs is
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;;; dumped. These variables' appropriate values depend on the conditions under
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;;; which the code is INVOKED; so it's inappropriate to initialize them when
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;;; Emacs is dumped---they should be initialized when calendar.el is loaded.
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;;; They default to US Eastern time if time zone info is not available.
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(calendar-current-time-zone)
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(defvar calendar-time-zone (car calendar-current-time-zone-cache)
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(defvar calendar-time-zone (or (car calendar-current-time-zone-cache) -300)
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"*Number of minutes difference between local standard time at
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`calendar-location-name' and Coordinated Universal (Greenwich) Time. For
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example, -300 for New York City, -480 for Los Angeles.")
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(defvar calendar-daylight-time-offset
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(car (cdr calendar-current-time-zone-cache))
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(or (car (cdr calendar-current-time-zone-cache)) 60)
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"*Number of minutes difference between daylight savings and standard time.
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If the locale never uses daylight savings time, set this to 0.")
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(defvar calendar-standard-time-zone-name
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(car (nthcdr 2 calendar-current-time-zone-cache))
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(or (car (nthcdr 2 calendar-current-time-zone-cache)) "EST")
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"*Abbreviated name of standard time zone at `calendar-location-name'.
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For example, \"EST\" in New York City, \"PST\" for Los Angeles.")
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(defvar calendar-daylight-time-zone-name
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(car (nthcdr 3 calendar-current-time-zone-cache))
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(or (car (nthcdr 3 calendar-current-time-zone-cache)) "EDT")
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"*Abbreviated name of daylight-savings time zone at `calendar-location-name'.
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For example, \"EDT\" in New York City, \"PDT\" for Los Angeles.")
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(defvar calendar-daylight-savings-starts
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(car (nthcdr 4 calendar-current-time-zone-cache))
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(or (car (nthcdr 4 calendar-current-time-zone-cache))
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(and (not (zerop calendar-daylight-time-offset))
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'(calendar-nth-named-day 1 0 4 year)))
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"*Sexp giving the date on which daylight savings time starts.
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This is an expression in the variable `year' whose value gives the Gregorian
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date in the form (month day year) on which daylight savings time starts. It is
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@ -310,7 +323,9 @@ because Nisan is the first month in the Hebrew calendar.
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If the locale never uses daylight savings time, set this to nil.")
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(defvar calendar-daylight-savings-ends
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(car (nthcdr 5 calendar-current-time-zone-cache))
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(or (car (nthcdr 5 calendar-current-time-zone-cache))
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(and (not (zerop calendar-daylight-time-offset))
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'(calendar-nth-named-day -1 0 10 year)))
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"*Sexp giving the date on which daylight savings time ends.
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This is an expression in the variable `year' whose value gives the Gregorian
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date in the form (month day year) on which daylight savings time ends. It is
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@ -327,10 +342,14 @@ begins:
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If the locale never uses daylight savings time, set this to nil.")
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(defvar calendar-daylight-savings-switchover-time
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(car (nthcdr 6 calendar-current-time-zone-cache))
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"*Number of minutes after midnight that daylight savings time begins/ends.
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If the locale never uses daylight savings time, set this to 0.")
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(defvar calendar-daylight-savings-starts-time
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(or (car (nthcdr 6 calendar-current-time-zone-cache)) 120)
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"*Number of minutes after midnight that daylight savings time starts.")
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(defvar calendar-daylight-savings-ends-time
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(or (car (nthcdr 7 calendar-current-time-zone-cache))
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calendar-daylight-savings-starts-time)
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"*Number of minutes after midnight that daylight savings time ends.")
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(provide 'cal-dst)
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