-;;; cal-dst.el --- calendar functions for daylight savings rules.
+;;; cal-dst.el --- calendar functions for daylight savings rules
-;; Copyright (C) 1993 Free Software Foundation, Inc.
+;; Copyright (C) 1993, 1994, 1995, 1996, 2001, 2002, 2003, 2004, 2005,
+;; 2006 Free Software Foundation, Inc.
;; Author: Paul Eggert <eggert@twinsun.com>
;; Edward M. Reingold <reingold@cs.uiuc.edu>
+;; Maintainer: Glenn Morris <rgm@gnu.org>
;; Keywords: calendar
;; Human-Keywords: daylight savings time, calendar, diary, holidays
;; This file is part of GNU Emacs.
+;; GNU Emacs is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 2, or (at your option)
+;; any later version.
+
;; GNU Emacs is distributed in the hope that it will be useful,
-;; but WITHOUT ANY WARRANTY. No author or distributor
-;; accepts responsibility to anyone for the consequences of using it
-;; or for whether it serves any particular purpose or works at all,
-;; unless he says so in writing. Refer to the GNU Emacs General Public
-;; License for full details.
-
-;; Everyone is granted permission to copy, modify and redistribute
-;; GNU Emacs, but only under the conditions described in the
-;; GNU Emacs General Public License. A copy of this license is
-;; supposed to have been given to you along with GNU Emacs so you
-;; can know your rights and responsibilities. It should be in a
-;; file named COPYING. Among other things, the copyright notice
-;; and this notice must be preserved on all copies.
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs; see the file COPYING. If not, write to the
+;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+;; Boston, MA 02110-1301, USA.
;;; Commentary:
;;; Code:
(require 'calendar)
+(require 'cal-persia)
+
+(defcustom calendar-dst-check-each-year-flag t
+ "Non-nil means to check each year for DST transitions as needed.
+nil means to assume the next two transitions found after the
+current date apply to all years. This is faster, but not always
+correct, since the dates of Daylight Saving transitions sometimes
+change."
+ :type 'boolean
+ :version "22.1"
+ :group 'calendar)
(defvar calendar-current-time-zone-cache nil
"Cache for result of calendar-current-time-zone.")
(let* ((h (car x))
(xtail (cdr x))
(l (+ utc-diff (if (numberp xtail) xtail (car xtail))))
- (u (+ (* 512 (% h 675)) (floor (/ l 128)))))
+ (u (+ (* 512 (mod h 675)) (floor l 128))))
;; Overflow is a terrible thing!
(cons (+ calendar-system-time-basis
;; floor((2^16 h +l) / (60*60*24))
- (* 512 (% h 675)) (floor (/ u 675)))
- ;; (2^16 h +l) % (60*60*24)
- (+ (* (% u 675) 128) (floor (% l 128))))))
+ (* 512 (floor h 675)) (floor u 675))
+ ;; (2^16 h +l) mod (60*60*24)
+ (+ (* (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.
-Returns the pair (HIGH . LOW) where HIGH and LOW are the high and low
+Returns the list (HIGH LOW) where HIGH and LOW are the high and low
16 bits, respectively, of the number of seconds 1970-01-01 00:00:00 UTC,
ignoring leap seconds, that is the equivalent moment to S seconds after
midnight UTC on absolute date ABS-DATE."
(let* ((a (- abs-date calendar-system-time-basis))
- (u (+ (* 163 (% a 512)) (floor (/ s 128)))))
+ (u (+ (* 163 (mod a 512)) (floor s 128))))
;; Overflow is a terrible thing!
- (cons
- ;; (60*60*24*a + s) / 2^16
- (+ a (* 163 (floor (/ a 512))) (floor (/ u 512)))
- ;; (60*60*24*a + s) % 2^16
- (+ (* 128 (% u 512)) (% s 128)))))
+ (list
+ ;; floor((60*60*24*a + s) / 2^16)
+ (+ a (* 163 (floor a 512)) (floor u 512))
+ ;; (60*60*24*a + s) mod 2^16
+ (+ (* 128 (mod u 512)) (mod s 128)))))
(defun calendar-next-time-zone-transition (time)
"Return the time of the next time zone transition after TIME.
(defun calendar-time-zone-daylight-rules (abs-date utc-diff)
"Return daylight transition rule for ABS-DATE, UTC-DIFF sec offset from UTC.
-ABS-DIFF must specify a day that contains a daylight savings transition.
+ABS-DATE must specify a day that contains a daylight savings transition.
The result has the proper form for calendar-daylight-savings-starts'."
(let* ((date (calendar-gregorian-from-absolute abs-date))
(weekday (% abs-date 7))
(list 'calendar-nth-named-day 1 weekday m 'year j)
l)))
l)
- ;; Israel is special.
- (if (zerop weekday)
- (if (< m 7)
- (list
- '(calendar-gregorian-from-absolute
- (calendar-dayname-on-or-before
- 0
- (calendar-absolute-from-hebrew
- (list 1 28 (+ year 3760))))))
- (list '(calendar-gregorian-from-absolute
- (calendar-dayname-on-or-before
- 0
- (- (calendar-absolute-from-hebrew
- (list 7 1 (+ year 3761))) 3))))))))
+ ;; 01-01 and 07-01 for this year's Persian calendar.
+ (if (and (= m 3) (<= 20 d) (<= d 21))
+ '((calendar-gregorian-from-absolute
+ (calendar-absolute-from-persian
+ (list 1 1 (- year 621))))))
+ (if (and (= m 9) (<= 22 d) (<= d 23))
+ '((calendar-gregorian-from-absolute
+ (calendar-absolute-from-persian
+ (list 7 1 (- year 621))))))))
(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)))
+
+;; TODO it might be better to extract this information directly from
+;; the system timezone database. But cross-platform...?
+;; See thread
+;; http://lists.gnu.org/archive/html/emacs-pretest-bug/2006-11/msg00060.html
+(defun calendar-dst-find-data (&optional time)
+ "Find data on the first Daylight Saving Time transitions after TIME.
+TIME defaults to `current-time'. Return value is as described
+for `calendar-current-time-zone'."
+ (let* ((t0 (or time (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))
+ ;; TODO When calendar-dst-check-each-year-flag is non-nil,
+ ;; the rules can be simpler than they currently are.
+ (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 t1-time t2-time)
+ (list t1-name t0-name t2-rules t1-rules t2-time t1-time)
+ )))))))))
+
+(defvar calendar-dst-transition-cache nil
+ "Internal cal-dst variable storing date of Daylight Saving Time transitions.
+Value is a list with elements of the form (YEAR START END), where
+START and END are expressions that when evaluated return the
+start and end dates (respectively) for DST in YEAR. Used by the
+function `calendar-dst-find-startend'.")
+
+(defun calendar-dst-find-startend (year)
+ "Find the dates in YEAR on which Daylight Saving Time starts and ends.
+Returns a list (YEAR START END), where START and END are
+expressions that when evaluated return the start and end dates,
+respectively. This function first attempts to use pre-calculated
+data from `calendar-dst-transition-cache', otherwise it calls
+`calendar-dst-find-data' (and adds the results to the cache)."
+ (let ((e (assoc year calendar-dst-transition-cache))
+ f)
+ (or e
+ (progn
+ (setq e (calendar-dst-find-data (encode-time 1 0 0 1 1 year))
+ f (nth 4 e)
+ e (list year f (nth 5 e))
+ calendar-dst-transition-cache
+ (append calendar-dst-transition-cache (list e)))
+ e))))
(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)
-
-;;; The following six defvars relating to daylight savings time should NOT be
+ (unless calendar-current-time-zone-cache
+ (setq calendar-current-time-zone-cache (calendar-dst-find-data))))
+
+;;; The following eight 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.")
-
+
+
+(defun calendar-dst-starts (year)
+ "Return the date of YEAR on which Daylight Saving Time starts.
+This function respects the value of `calendar-dst-check-each-year-flag'."
+ (or (let ((expr (if calendar-dst-check-each-year-flag
+ (cadr (calendar-dst-find-startend year))
+ (nth 4 calendar-current-time-zone-cache))))
+ (if expr (eval expr)))
+ (and (not (zerop calendar-daylight-time-offset))
+ (calendar-nth-named-day 1 0 4 year))))
+
+(defun calendar-dst-ends (year)
+ "Return the date of YEAR on which Daylight Saving Time ends.
+This function respects the value of `calendar-dst-check-each-year-flag'."
+ (or (let ((expr (if calendar-dst-check-each-year-flag
+ (nth 2 (calendar-dst-find-startend year))
+ (nth 5 calendar-current-time-zone-cache))))
+ (if expr (eval expr)))
+ (and (not (zerop calendar-daylight-time-offset))
+ (calendar-nth-named-day -1 0 10 year))))
+
+
+;;;###autoload
+(put 'calendar-daylight-savings-starts 'risky-local-variable t)
(defvar calendar-daylight-savings-starts
- (car (nthcdr 4 calendar-current-time-zone-cache))
+ '(calendar-dst-starts 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
'(10 1 year)
-For a more complex example, daylight savings time begins in Israel on the
-first Sunday after Passover ends on Nisan 21:
-
- '(calendar-gregorian-from-absolute
- (calendar-dayname-on-or-before
- 0
- (calendar-absolute-from-hebrew (list 1 28 (+ year 3760)))))
+If it starts on the first Sunday in April, you would set it to
-because Nisan is the first month in the Hebrew calendar.
+ '(calendar-nth-named-day 1 0 4 year)
If the locale never uses daylight savings time, set this to nil.")
+;;;###autoload
+(put 'calendar-daylight-savings-ends 'risky-local-variable t)
(defvar calendar-daylight-savings-ends
- (car (nthcdr 5 calendar-current-time-zone-cache))
+ '(calendar-dst-ends 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
used to determine the starting date of daylight savings time for the holiday
list and for correcting times of day in the solar and lunar calculations.
-For example, daylight savings time ends in Israel on the Sunday Selichot
-begins:
+For example, if daylight savings time ends on the last Sunday in October:
- '(calendar-gregorian-from-absolute
- (calendar-dayname-on-or-before
- 0
- (- (calendar-absolute-from-hebrew (list 7 1 (+ year 3761))) 3)))
+ '(calendar-nth-named-day -1 0 10 year)
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.")
+
+(defun dst-in-effect (date)
+ "True if on absolute DATE daylight savings time is in effect.
+Fractional part of DATE is local standard time of day."
+ (let* ((year (extract-calendar-year
+ (calendar-gregorian-from-absolute (floor date))))
+ (dst-starts-gregorian (eval calendar-daylight-savings-starts))
+ (dst-ends-gregorian (eval calendar-daylight-savings-ends))
+ (dst-starts (and dst-starts-gregorian
+ (+ (calendar-absolute-from-gregorian
+ dst-starts-gregorian)
+ (/ calendar-daylight-savings-starts-time
+ 60.0 24.0))))
+ (dst-ends (and dst-ends-gregorian
+ (+ (calendar-absolute-from-gregorian
+ dst-ends-gregorian)
+ (/ (- calendar-daylight-savings-ends-time
+ calendar-daylight-time-offset)
+ 60.0 24.0)))))
+ (and dst-starts dst-ends
+ (if (< dst-starts dst-ends)
+ (and (<= dst-starts date) (< date dst-ends))
+ (or (<= dst-starts date) (< date dst-ends))))))
+
+(defun dst-adjust-time (date time &optional style)
+ "Adjust, to account for dst on DATE, decimal fraction standard TIME.
+Returns a list (date adj-time zone) where `date' and `adj-time' are the values
+adjusted for `zone'; here `date' is a list (month day year), `adj-time' is a
+decimal fraction time, and `zone' is a string.
+
+Optional parameter STYLE forces the result time to be standard time when its
+value is 'standard and daylight savings time (if available) when its value is
+'daylight.
+
+Conversion to daylight savings time is done according to
+`calendar-daylight-savings-starts', `calendar-daylight-savings-ends',
+`calendar-daylight-savings-starts-time',
+`calendar-daylight-savings-ends-time', and
+`calendar-daylight-savings-offset'."
+
+ (let* ((rounded-abs-date (+ (calendar-absolute-from-gregorian date)
+ (/ (round (* 60 time)) 60.0 24.0)))
+ (dst (dst-in-effect rounded-abs-date))
+ (time-zone (if dst
+ calendar-daylight-time-zone-name
+ calendar-standard-time-zone-name))
+ (time (+ rounded-abs-date
+ (if dst (/ calendar-daylight-time-offset 24.0 60.0) 0))))
+ (list (calendar-gregorian-from-absolute (truncate time))
+ (* 24.0 (- time (truncate time)))
+ time-zone)))
(provide 'cal-dst)
+;;; arch-tag: a141d204-213c-4ca5-bdc6-f9df3aa92aad
;;; cal-dst.el ends here