;; Overflow is a terrible thing!
(cons (+ calendar-system-time-basis
;; floor((2^16 h +l) / (60*60*24))
- (* 512 (mod h 675)) (floor u 675))
+ (* 512 (floor h 675)) (floor u 675))
;; (2^16 h +l) % (60*60*24)
- (+ (* (mod u 675) 128) (floor l 128)))))
+ (+ (* (mod u 675) 128) (mod l 128)))))
(defun calendar-time-from-absolute (abs-date s)
"Time of absolute date ABS-DATE, S seconds after midnight.
(- (calendar-absolute-from-hebrew
(list 7 1 (+ year 3761))) 3))))))))
(prevday-sec (- -1 utc-diff)) ;; last sec of previous local day
- last-surviving-rule
- (i 1))
- ;; Scan through the next few years; take the rule that explains them best.
- (while (and candidate-rules (cdr candidate-rules) (<= i 28))
- (let ((year (+ y i))
- new-rules)
- (while candidate-rules
- (let* ((rule (car candidate-rules))
- (date (calendar-absolute-from-gregorian (eval rule))))
- (or (equal (current-time-zone
- (calendar-time-from-absolute date prevday-sec))
- (current-time-zone
- (calendar-time-from-absolute (1+ date) prevday-sec)))
- (progn
- (setq new-rules (cons rule new-rules))
- (setq last-surviving-rule rule))))
- (setq candidate-rules (cdr candidate-rules)))
- (setq candidate-rules (nreverse new-rules)))
- (setq i (1+ i)))
- last-surviving-rule))
+ (year (1+ y)))
+ ;; Scan through the next few years until only one rule remains.
+ (while
+ (let ((rules candidate-rules)
+ new-rules)
+ (while
+ (let*
+ ((rule (car rules))
+ (date
+ ;; The following is much faster than
+ ;; (calendar-absolute-from-gregorian (eval rule)).
+ (cond ((eq (car rule) 'calendar-nth-named-day)
+ (eval (cons 'calendar-nth-named-absday (cdr rule))))
+ ((eq (car rule) 'calendar-gregorian-from-absolute)
+ (eval (car (cdr rule))))
+ (t (let ((g (eval rule)))
+ (calendar-absolute-from-gregorian g))))))
+ (or (equal
+ (current-time-zone
+ (calendar-time-from-absolute date prevday-sec))
+ (current-time-zone
+ (calendar-time-from-absolute (1+ date) prevday-sec)))
+ (setq new-rules (cons rule new-rules)))
+ (setq rules (cdr rules))))
+ ;; If no rules remain, just use the first candidate rule;
+ ;; it's wrong in general, but it's right for at least one year.
+ (setq candidate-rules (if new-rules (nreverse new-rules)
+ (list (car candidate-rules))))
+ (setq year (1+ year))
+ (cdr candidate-rules)))
+ (car candidate-rules)))
(defun calendar-current-time-zone ()
"Return UTC difference, dst offset, names and rules for current time zone.
-Returns (UTC-DIFF DST-OFFSET STD-ZONE DST-ZONE DST-STARTS DST-ENDS DST-SWITCH),
-based on a heuristic probing of what the system knows:
+Returns (UTC-DIFF DST-OFFSET STD-ZONE DST-ZONE DST-STARTS DST-ENDS
+DST-STARTS-TIME DST-ENDS-TIME), based on a heuristic probing of what the
+system knows:
UTC-DIFF is an integer specifying the number of minutes difference between
standard time in the current time zone and Coordinated Universal Time
DST-ZONE is a string giving the name of the time zone when there is a seasonal
time adjustment in effect.
DST-STARTS and DST-ENDS are sexps in the variable `year' giving the daylight
- savings time start rules, in the form expected by
+ savings time start and end rules, in the form expected by
`calendar-daylight-savings-starts'.
-DST-SWITCH is an integer giving the number of minutes after midnight that
- daylight savings time starts or ends.
+DST-STARTS-TIME and DST-ENDS-TIME are integers giving the number of minutes
+ after midnight that daylight savings time starts and ends.
-If the local area does not use a seasonal time adjustment, DST-OFFSET and
-DST-SWITCH are 0, STD-ZONE and DST-ZONE are equal, and DST-STARTS and DST-ENDS
-are nil.
+If the local area does not use a seasonal time adjustment, STD-ZONE and
+DST-ZONE are equal, and all the DST-* integer variables are 0.
Some operating systems cannot provide all this information to Emacs; in this
case, `calendar-current-time-zone' returns a list containing nil for the data
it can't find."
(or
calendar-current-time-zone-cache
- (progn
- (message "Checking time zone data...")
- (setq
- calendar-current-time-zone-cache
- (let* ((now (current-time))
- (now-zone (current-time-zone now))
- (now-utc-diff (car now-zone))
- (now-name (car (cdr now-zone)))
- (next (calendar-next-time-zone-transition now)))
- (if (null next)
- (list (and now-utc-diff (/ now-utc-diff 60))
- 0 now-name now-name nil nil 0)
- (let* ((next-zone (current-time-zone next))
- (next-utc-diff (car next-zone))
- (next-name (car (cdr next-zone)))
- (next-absdate-seconds
- (calendar-absolute-from-time next now-utc-diff))
- (next-transitions
- (calendar-time-zone-daylight-rules
- (car next-absdate-seconds) now-utc-diff))
- (nextnext (calendar-next-time-zone-transition next))
- (now-transitions
- (calendar-time-zone-daylight-rules
- (car (calendar-absolute-from-time nextnext next-utc-diff))
- next-utc-diff))
- (now-is-std (< now-utc-diff next-utc-diff)))
- (list (/ (min now-utc-diff next-utc-diff) 60)
- (/ (abs (- now-utc-diff next-utc-diff)) 60)
- (if now-is-std now-name next-name)
- (if now-is-std next-name now-name)
- (if now-is-std next-transitions now-transitions)
- (if now-is-std now-transitions next-transitions)
- (/ (cdr next-absdate-seconds) 60))))))
- (message "Checking time zone data...done")))
- calendar-current-time-zone-cache)
+ (setq
+ calendar-current-time-zone-cache
+ (let* ((t0 (current-time))
+ (t0-zone (current-time-zone t0))
+ (t0-utc-diff (car t0-zone))
+ (t0-name (car (cdr t0-zone))))
+ (if (not t0-utc-diff)
+ ;; Little or no time zone information is available.
+ (list nil nil t0-name t0-name nil nil nil nil)
+ (let* ((t1 (calendar-next-time-zone-transition t0))
+ (t2 (and t1 (calendar-next-time-zone-transition t1))))
+ (if (not t2)
+ ;; This locale does not have daylight savings time.
+ (list (/ t0-utc-diff 60) 0 t0-name t0-name nil nil 0 0)
+ ;; Use heuristics to find daylight savings parameters.
+ (let* ((t1-zone (current-time-zone t1))
+ (t1-utc-diff (car t1-zone))
+ (t1-name (car (cdr t1-zone)))
+ (t1-date-sec (calendar-absolute-from-time t1 t0-utc-diff))
+ (t2-date-sec (calendar-absolute-from-time t2 t1-utc-diff))
+ (t1-rules (calendar-time-zone-daylight-rules
+ (car t1-date-sec) t0-utc-diff))
+ (t2-rules (calendar-time-zone-daylight-rules
+ (car t2-date-sec) t1-utc-diff))
+ (t1-time (/ (cdr t1-date-sec) 60))
+ (t2-time (/ (cdr t2-date-sec) 60)))
+ (cons
+ (/ (min t0-utc-diff t1-utc-diff) 60)
+ (cons
+ (/ (abs (- t0-utc-diff t1-utc-diff)) 60)
+ (if (< t0-utc-diff t1-utc-diff)
+ (list t0-name t1-name t1-rules t2-rules t2-time t1-time)
+ (list t1-name t0-name t2-rules t1-rules t1-time t2-time)
+ )))))))))))
;;; The following six defvars relating to daylight savings time should NOT be
;;; marked to go into loaddefs.el where they would be evaluated when Emacs is
;;; dumped. These variables' appropriate values depend on the conditions under
;;; which the code is INVOKED; so it's inappropriate to initialize them when
;;; Emacs is dumped---they should be initialized when calendar.el is loaded.
+;;; They default to US Eastern time if time zone info is not available.
(calendar-current-time-zone)
-(defvar calendar-time-zone (car calendar-current-time-zone-cache)
+(defvar calendar-time-zone (or (car calendar-current-time-zone-cache) -300)
"*Number of minutes difference between local standard time at
`calendar-location-name' and Coordinated Universal (Greenwich) Time. For
example, -300 for New York City, -480 for Los Angeles.")
(defvar calendar-daylight-time-offset
- (car (cdr calendar-current-time-zone-cache))
+ (or (car (cdr calendar-current-time-zone-cache)) 60)
"*Number of minutes difference between daylight savings and standard time.
If the locale never uses daylight savings time, set this to 0.")
(defvar calendar-standard-time-zone-name
- (car (nthcdr 2 calendar-current-time-zone-cache))
+ (or (car (nthcdr 2 calendar-current-time-zone-cache)) "EST")
"*Abbreviated name of standard time zone at `calendar-location-name'.
For example, \"EST\" in New York City, \"PST\" for Los Angeles.")
(defvar calendar-daylight-time-zone-name
- (car (nthcdr 3 calendar-current-time-zone-cache))
+ (or (car (nthcdr 3 calendar-current-time-zone-cache)) "EDT")
"*Abbreviated name of daylight-savings time zone at `calendar-location-name'.
For example, \"EDT\" in New York City, \"PDT\" for Los Angeles.")
(defvar calendar-daylight-savings-starts
- (car (nthcdr 4 calendar-current-time-zone-cache))
+ (or (car (nthcdr 4 calendar-current-time-zone-cache))
+ (and (not (zerop calendar-daylight-time-offset))
+ '(calendar-nth-named-day 1 0 4 year)))
"*Sexp giving the date on which daylight savings time starts.
This is an expression in the variable `year' whose value gives the Gregorian
date in the form (month day year) on which daylight savings time starts. It is
If the locale never uses daylight savings time, set this to nil.")
(defvar calendar-daylight-savings-ends
- (car (nthcdr 5 calendar-current-time-zone-cache))
+ (or (car (nthcdr 5 calendar-current-time-zone-cache))
+ (and (not (zerop calendar-daylight-time-offset))
+ '(calendar-nth-named-day -1 0 10 year)))
"*Sexp giving the date on which daylight savings time ends.
This is an expression in the variable `year' whose value gives the Gregorian
date in the form (month day year) on which daylight savings time ends. It is
If the locale never uses daylight savings time, set this to nil.")
-(defvar calendar-daylight-savings-switchover-time
- (car (nthcdr 6 calendar-current-time-zone-cache))
- "*Number of minutes after midnight that daylight savings time begins/ends.
-If the locale never uses daylight savings time, set this to 0.")
+(defvar calendar-daylight-savings-starts-time
+ (or (car (nthcdr 6 calendar-current-time-zone-cache)) 120)
+ "*Number of minutes after midnight that daylight savings time starts.")
+
+(defvar calendar-daylight-savings-ends-time
+ (or (car (nthcdr 7 calendar-current-time-zone-cache))
+ calendar-daylight-savings-starts-time)
+ "*Number of minutes after midnight that daylight savings time ends.")
(provide 'cal-dst)