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e716fd62 | 1 | ;;; cal-dst.el --- calendar functions for daylight saving rules |
3e03d7c7 | 2 | |
ba318903 | 3 | ;; Copyright (C) 1993-1996, 2001-2014 Free Software Foundation, Inc. |
3e03d7c7 JB |
4 | |
5 | ;; Author: Paul Eggert <eggert@twinsun.com> | |
71ea27ee | 6 | ;; Edward M. Reingold <reingold@cs.uiuc.edu> |
dbfca9c4 | 7 | ;; Maintainer: Glenn Morris <rgm@gnu.org> |
3e03d7c7 | 8 | ;; Keywords: calendar |
e716fd62 | 9 | ;; Human-Keywords: daylight saving time, calendar, diary, holidays |
bd78fa1d | 10 | ;; Package: calendar |
3e03d7c7 JB |
11 | |
12 | ;; This file is part of GNU Emacs. | |
13 | ||
2ed66575 | 14 | ;; GNU Emacs is free software: you can redistribute it and/or modify |
59243403 | 15 | ;; it under the terms of the GNU General Public License as published by |
2ed66575 GM |
16 | ;; the Free Software Foundation, either version 3 of the License, or |
17 | ;; (at your option) any later version. | |
59243403 | 18 | |
3e03d7c7 | 19 | ;; GNU Emacs is distributed in the hope that it will be useful, |
59243403 RS |
20 | ;; but WITHOUT ANY WARRANTY; without even the implied warranty of |
21 | ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
22 | ;; GNU General Public License for more details. | |
23 | ||
24 | ;; You should have received a copy of the GNU General Public License | |
2ed66575 | 25 | ;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>. |
3e03d7c7 JB |
26 | |
27 | ;;; Commentary: | |
28 | ||
b1c57079 | 29 | ;; See calendar.el. |
3e03d7c7 | 30 | |
3e03d7c7 JB |
31 | ;;; Code: |
32 | ||
33 | (require 'calendar) | |
34 | ||
ec1ee609 GM |
35 | |
36 | (defgroup calendar-dst nil | |
37 | "Options related to Daylight Saving Time." | |
38 | :prefix "calendar-" | |
39 | :group 'calendar) | |
40 | ||
41 | ||
cd72c399 GM |
42 | (defcustom calendar-dst-check-each-year-flag t |
43 | "Non-nil means to check each year for DST transitions as needed. | |
f3f4e600 | 44 | Otherwise assume the next two transitions found after the |
cd72c399 | 45 | current date apply to all years. This is faster, but not always |
e716fd62 | 46 | correct, since the dates of daylight saving transitions sometimes |
cd72c399 GM |
47 | change." |
48 | :type 'boolean | |
49 | :version "22.1" | |
76db8823 | 50 | :group 'calendar-dst) |
cd72c399 | 51 | |
ec1ee609 GM |
52 | ;;;###autoload |
53 | (put 'calendar-daylight-savings-starts 'risky-local-variable t) | |
54 | (defcustom calendar-daylight-savings-starts '(calendar-dst-starts year) | |
55 | "Sexp giving the date on which daylight saving time starts. | |
56 | This is an expression in the variable `year' whose value gives the Gregorian | |
57 | date in the form (month day year) on which daylight saving time starts. It is | |
58 | used to determine the starting date of daylight saving time for the holiday | |
59 | list and for correcting times of day in the solar and lunar calculations. | |
60 | ||
61 | For example, if daylight saving time is mandated to start on October 1, | |
62 | you would set `calendar-daylight-savings-starts' to | |
63 | ||
64 | '(10 1 year) | |
65 | ||
66 | If it starts on the first Sunday in April, you would set it to | |
67 | ||
68 | '(calendar-nth-named-day 1 0 4 year) | |
69 | ||
70 | If the locale never uses daylight saving time, set this to nil." | |
71 | :type 'sexp | |
72 | :group 'calendar-dst) | |
73 | ||
74 | ;;;###autoload | |
75 | (put 'calendar-daylight-savings-ends 'risky-local-variable t) | |
76 | (defcustom calendar-daylight-savings-ends '(calendar-dst-ends year) | |
77 | "Sexp giving the date on which daylight saving time ends. | |
78 | This is an expression in the variable `year' whose value gives the Gregorian | |
79 | date in the form (month day year) on which daylight saving time ends. It is | |
80 | used to determine the starting date of daylight saving time for the holiday | |
81 | list and for correcting times of day in the solar and lunar calculations. | |
82 | ||
83 | For example, if daylight saving time ends on the last Sunday in October: | |
84 | ||
85 | '(calendar-nth-named-day -1 0 10 year) | |
86 | ||
87 | If the locale never uses daylight saving time, set this to nil." | |
88 | :type 'sexp | |
89 | :group 'calendar-dst) | |
90 | ||
91 | ;;; More defcustoms below. | |
92 | ||
93 | ||
3e03d7c7 | 94 | (defvar calendar-current-time-zone-cache nil |
ed589f9a | 95 | "Cache for result of `calendar-current-time-zone'.") |
76db8823 GM |
96 | ;; It gets eval'd, eg by calendar-dst-starts. |
97 | ;;;###autoload | |
98 | (put 'calendar-current-time-zone-cache 'risky-local-variable t) | |
3e03d7c7 JB |
99 | |
100 | (defvar calendar-system-time-basis | |
101 | (calendar-absolute-from-gregorian '(1 1 1970)) | |
102 | "Absolute date of starting date of system clock.") | |
103 | ||
3e03d7c7 JB |
104 | (defun calendar-absolute-from-time (x utc-diff) |
105 | "Absolute local date of time X; local time is UTC-DIFF seconds from UTC. | |
106 | ||
107 | X is (HIGH . LOW) or (HIGH LOW . IGNORED) where HIGH and LOW are the | |
108 | high and low 16 bits, respectively, of the number of seconds since | |
109 | 1970-01-01 00:00:00 UTC, ignoring leap seconds. | |
110 | ||
111 | Returns the pair (ABS-DATE . SECONDS) where SECONDS after local midnight on | |
112 | absolute date ABS-DATE is the equivalent moment to X." | |
113 | (let* ((h (car x)) | |
71ea27ee | 114 | (xtail (cdr x)) |
3e03d7c7 | 115 | (l (+ utc-diff (if (numberp xtail) xtail (car xtail)))) |
4cc1b78a | 116 | (u (+ (* 512 (mod h 675)) (floor l 128)))) |
3e03d7c7 JB |
117 | ;; Overflow is a terrible thing! |
118 | (cons (+ calendar-system-time-basis | |
71ea27ee GM |
119 | ;; floor((2^16 h +l) / (60*60*24)) |
120 | (* 512 (floor h 675)) (floor u 675)) | |
121 | ;; (2^16 h +l) mod (60*60*24) | |
122 | (+ (* (mod u 675) 128) (mod l 128))))) | |
3e03d7c7 JB |
123 | |
124 | (defun calendar-time-from-absolute (abs-date s) | |
125 | "Time of absolute date ABS-DATE, S seconds after midnight. | |
126 | ||
ec9b5635 | 127 | Returns the list (HIGH LOW) where HIGH and LOW are the high and low |
3e03d7c7 JB |
128 | 16 bits, respectively, of the number of seconds 1970-01-01 00:00:00 UTC, |
129 | ignoring leap seconds, that is the equivalent moment to S seconds after | |
130 | midnight UTC on absolute date ABS-DATE." | |
131 | (let* ((a (- abs-date calendar-system-time-basis)) | |
4cc1b78a | 132 | (u (+ (* 163 (mod a 512)) (floor s 128)))) |
3e03d7c7 | 133 | ;; Overflow is a terrible thing! |
ec9b5635 | 134 | (list |
3ac14ca0 | 135 | ;; floor((60*60*24*a + s) / 2^16) |
4cc1b78a | 136 | (+ a (* 163 (floor a 512)) (floor u 512)) |
3ac14ca0 | 137 | ;; (60*60*24*a + s) mod 2^16 |
4cc1b78a | 138 | (+ (* 128 (mod u 512)) (mod s 128))))) |
3e03d7c7 JB |
139 | |
140 | (defun calendar-next-time-zone-transition (time) | |
141 | "Return the time of the next time zone transition after TIME. | |
311cc551 | 142 | Both TIME and the result are acceptable arguments to `current-time-zone'. |
3e03d7c7 | 143 | Return nil if no such transition can be found." |
fd32e5b9 GM |
144 | (let* ((base 65536) ; 2^16 = base of current-time output |
145 | (quarter-multiple 120) ; approx = (seconds per quarter year) / base | |
71ea27ee GM |
146 | (time-zone (current-time-zone time)) |
147 | (time-utc-diff (car time-zone)) | |
3e03d7c7 | 148 | hi |
71ea27ee | 149 | hi-zone |
3e03d7c7 JB |
150 | (hi-utc-diff time-utc-diff) |
151 | (quarters '(2 1 3))) | |
152 | ;; Heuristic: probe the time zone offset in the next three calendar | |
153 | ;; quarters, looking for a time zone offset different from TIME. | |
154 | (while (and quarters (eq time-utc-diff hi-utc-diff)) | |
4b8683c7 GM |
155 | (setq hi (cons (+ (car time) (* (car quarters) quarter-multiple)) 0) |
156 | hi-zone (current-time-zone hi) | |
157 | hi-utc-diff (car hi-zone) | |
158 | quarters (cdr quarters))) | |
3e03d7c7 JB |
159 | (and |
160 | time-utc-diff | |
161 | hi-utc-diff | |
162 | (not (eq time-utc-diff hi-utc-diff)) | |
163 | ;; Now HI is after the next time zone transition. | |
164 | ;; Set LO to TIME, and then binary search to increase LO and decrease HI | |
165 | ;; until LO is just before and HI is just after the time zone transition. | |
166 | (let* ((tail (cdr time)) | |
71ea27ee GM |
167 | (lo (cons (car time) (if (numberp tail) tail (car tail)))) |
168 | probe) | |
3e03d7c7 | 169 | (while |
71ea27ee GM |
170 | ;; Set PROBE to halfway between LO and HI, rounding down. |
171 | ;; If PROBE equals LO, we are done. | |
172 | (let* ((lsum (+ (cdr lo) (cdr hi))) | |
173 | (hsum (+ (car lo) (car hi) (/ lsum base))) | |
174 | (hsumodd (logand 1 hsum))) | |
175 | (setq probe (cons (/ (- hsum hsumodd) 2) | |
176 | (/ (+ (* hsumodd base) (% lsum base)) 2))) | |
177 | (not (equal lo probe))) | |
178 | ;; Set either LO or HI to PROBE, depending on probe results. | |
179 | (if (eq (car (current-time-zone probe)) hi-utc-diff) | |
180 | (setq hi probe) | |
181 | (setq lo probe))) | |
3e03d7c7 JB |
182 | hi)))) |
183 | ||
d80c2c18 | 184 | (autoload 'calendar-persian-to-absolute "cal-persia") |
06e3b7ae | 185 | |
3e03d7c7 JB |
186 | (defun calendar-time-zone-daylight-rules (abs-date utc-diff) |
187 | "Return daylight transition rule for ABS-DATE, UTC-DIFF sec offset from UTC. | |
e716fd62 CY |
188 | ABS-DATE must specify a day that contains a daylight saving transition. |
189 | The result has the proper form for `calendar-daylight-savings-starts'." | |
3e03d7c7 | 190 | (let* ((date (calendar-gregorian-from-absolute abs-date)) |
71ea27ee | 191 | (weekday (% abs-date 7)) |
e803eab7 GM |
192 | (m (calendar-extract-month date)) |
193 | (d (calendar-extract-day date)) | |
194 | (y (calendar-extract-year date)) | |
3e03d7c7 | 195 | (last (calendar-last-day-of-month m y)) |
ff35f3b8 GM |
196 | j rlist |
197 | (candidate-rules ; these return Gregorian dates | |
71ea27ee GM |
198 | (append |
199 | ;; Day D of month M. | |
ff35f3b8 | 200 | `((list ,m ,d year)) |
71ea27ee | 201 | ;; The first WEEKDAY of month M. |
3e03d7c7 | 202 | (if (< d 8) |
ff35f3b8 | 203 | `((calendar-nth-named-day 1 ,weekday ,m year))) |
71ea27ee | 204 | ;; The last WEEKDAY of month M. |
3e03d7c7 | 205 | (if (> d (- last 7)) |
ff35f3b8 GM |
206 | `((calendar-nth-named-day -1 ,weekday ,m year))) |
207 | (progn | |
208 | ;; The first WEEKDAY after day J of month M, for D-6 < J <= D. | |
209 | (setq j (1- (max 2 (- d 6)))) | |
210 | (while (<= (setq j (1+ j)) (min d (- last 8))) | |
211 | (push `(calendar-nth-named-day 1 ,weekday ,m year ,j) rlist)) | |
212 | rlist) | |
71ea27ee | 213 | ;; 01-01 and 07-01 for this year's Persian calendar. |
ff35f3b8 | 214 | ;; FIXME what does the Persian calendar have to do with this? |
84cb770d GM |
215 | (and (= m 3) (memq d '(20 21)) |
216 | '((calendar-gregorian-from-absolute | |
217 | (calendar-persian-to-absolute `(1 1 ,(- year 621)))))) | |
218 | (and (= m 9) (memq d '(22 23)) | |
219 | '((calendar-gregorian-from-absolute | |
220 | (calendar-persian-to-absolute `(7 1 ,(- year 621)))))))) | |
fd32e5b9 | 221 | (prevday-sec (- -1 utc-diff)) ; last sec of previous local day |
ff35f3b8 GM |
222 | (year (1+ y)) |
223 | new-rules) | |
6bc457fe | 224 | ;; Scan through the next few years until only one rule remains. |
ff35f3b8 GM |
225 | (while (cdr candidate-rules) |
226 | (dolist (rule candidate-rules) | |
227 | ;; The rule we return should give a Gregorian date, but here | |
228 | ;; we require an absolute date. The following is for efficiency. | |
229 | (setq date (cond ((eq (car rule) 'calendar-nth-named-day) | |
230 | (eval (cons 'calendar-nth-named-absday (cdr rule)))) | |
231 | ((eq (car rule) 'calendar-gregorian-from-absolute) | |
b27c3bc6 | 232 | (eval (cadr rule))) |
ff35f3b8 GM |
233 | (t (calendar-absolute-from-gregorian (eval rule))))) |
234 | (or (equal (current-time-zone | |
235 | (calendar-time-from-absolute date prevday-sec)) | |
236 | (current-time-zone | |
237 | (calendar-time-from-absolute (1+ date) prevday-sec))) | |
238 | (setq new-rules (cons rule new-rules)))) | |
239 | ;; If no rules remain, just use the first candidate rule; | |
240 | ;; it's wrong in general, but it's right for at least one year. | |
241 | (setq candidate-rules (if new-rules (nreverse new-rules) | |
242 | (list (car candidate-rules))) | |
4f1c166c GM |
243 | new-rules nil |
244 | year (1+ year))) | |
6bc457fe | 245 | (car candidate-rules))) |
3e03d7c7 | 246 | |
cd72c399 GM |
247 | ;; TODO it might be better to extract this information directly from |
248 | ;; the system timezone database. But cross-platform...? | |
249 | ;; See thread | |
250 | ;; http://lists.gnu.org/archive/html/emacs-pretest-bug/2006-11/msg00060.html | |
251 | (defun calendar-dst-find-data (&optional time) | |
e716fd62 | 252 | "Find data on the first daylight saving time transitions after TIME. |
cd72c399 GM |
253 | TIME defaults to `current-time'. Return value is as described |
254 | for `calendar-current-time-zone'." | |
255 | (let* ((t0 (or time (current-time))) | |
256 | (t0-zone (current-time-zone t0)) | |
257 | (t0-utc-diff (car t0-zone)) | |
4b8683c7 | 258 | (t0-name (cadr t0-zone))) |
cd72c399 GM |
259 | (if (not t0-utc-diff) |
260 | ;; Little or no time zone information is available. | |
261 | (list nil nil t0-name t0-name nil nil nil nil) | |
262 | (let* ((t1 (calendar-next-time-zone-transition t0)) | |
263 | (t2 (and t1 (calendar-next-time-zone-transition t1)))) | |
264 | (if (not t2) | |
e716fd62 | 265 | ;; This locale does not have daylight saving time. |
cd72c399 | 266 | (list (/ t0-utc-diff 60) 0 t0-name t0-name nil nil 0 0) |
e716fd62 | 267 | ;; Use heuristics to find daylight saving parameters. |
cd72c399 GM |
268 | (let* ((t1-zone (current-time-zone t1)) |
269 | (t1-utc-diff (car t1-zone)) | |
4b8683c7 | 270 | (t1-name (cadr t1-zone)) |
cd72c399 GM |
271 | (t1-date-sec (calendar-absolute-from-time t1 t0-utc-diff)) |
272 | (t2-date-sec (calendar-absolute-from-time t2 t1-utc-diff)) | |
273 | ;; TODO When calendar-dst-check-each-year-flag is non-nil, | |
274 | ;; the rules can be simpler than they currently are. | |
275 | (t1-rules (calendar-time-zone-daylight-rules | |
276 | (car t1-date-sec) t0-utc-diff)) | |
277 | (t2-rules (calendar-time-zone-daylight-rules | |
278 | (car t2-date-sec) t1-utc-diff)) | |
279 | (t1-time (/ (cdr t1-date-sec) 60)) | |
280 | (t2-time (/ (cdr t2-date-sec) 60))) | |
281 | (cons | |
282 | (/ (min t0-utc-diff t1-utc-diff) 60) | |
283 | (cons | |
284 | (/ (abs (- t0-utc-diff t1-utc-diff)) 60) | |
285 | (if (< t0-utc-diff t1-utc-diff) | |
286 | (list t0-name t1-name t1-rules t2-rules t1-time t2-time) | |
287 | (list t1-name t0-name t2-rules t1-rules t2-time t1-time) | |
288 | ))))))))) | |
289 | ||
290 | (defvar calendar-dst-transition-cache nil | |
e716fd62 | 291 | "Internal cal-dst variable storing date of daylight saving time transitions. |
cd72c399 GM |
292 | Value is a list with elements of the form (YEAR START END), where |
293 | START and END are expressions that when evaluated return the | |
311cc551 | 294 | start and end dates (respectively) for DST in YEAR. Used by the |
cd72c399 GM |
295 | function `calendar-dst-find-startend'.") |
296 | ||
297 | (defun calendar-dst-find-startend (year) | |
e716fd62 | 298 | "Find the dates in YEAR on which daylight saving time starts and ends. |
cd72c399 GM |
299 | Returns a list (YEAR START END), where START and END are |
300 | expressions that when evaluated return the start and end dates, | |
301 | respectively. This function first attempts to use pre-calculated | |
302 | data from `calendar-dst-transition-cache', otherwise it calls | |
325c2dd1 GM |
303 | `calendar-dst-find-data' (and adds the results to the cache). |
304 | If dates in YEAR cannot be handled by `encode-time' (e.g. if they | |
305 | are too large to be represented as a lisp integer), then rather | |
306 | than an error this function returns the result appropriate for | |
307 | the current year." | |
cd72c399 GM |
308 | (let ((e (assoc year calendar-dst-transition-cache)) |
309 | f) | |
310 | (or e | |
311 | (progn | |
325c2dd1 GM |
312 | (setq e (calendar-dst-find-data |
313 | (condition-case nil | |
314 | (encode-time 1 0 0 1 1 year) | |
315 | (error | |
316 | (encode-time 1 0 0 1 1 (nth 5 (decode-time)))))) | |
cd72c399 GM |
317 | f (nth 4 e) |
318 | e (list year f (nth 5 e)) | |
319 | calendar-dst-transition-cache | |
320 | (append calendar-dst-transition-cache (list e))) | |
321 | e)))) | |
322 | ||
3e03d7c7 JB |
323 | (defun calendar-current-time-zone () |
324 | "Return UTC difference, dst offset, names and rules for current time zone. | |
325 | ||
6bc457fe PE |
326 | Returns (UTC-DIFF DST-OFFSET STD-ZONE DST-ZONE DST-STARTS DST-ENDS |
327 | DST-STARTS-TIME DST-ENDS-TIME), based on a heuristic probing of what the | |
328 | system knows: | |
3e03d7c7 JB |
329 | |
330 | UTC-DIFF is an integer specifying the number of minutes difference between | |
331 | standard time in the current time zone and Coordinated Universal Time | |
332 | (Greenwich Mean Time). A negative value means west of Greenwich. | |
e716fd62 | 333 | DST-OFFSET is an integer giving the daylight saving time offset in minutes. |
3e03d7c7 JB |
334 | STD-ZONE is a string giving the name of the time zone when no seasonal time |
335 | adjustment is in effect. | |
336 | DST-ZONE is a string giving the name of the time zone when there is a seasonal | |
337 | time adjustment in effect. | |
338 | DST-STARTS and DST-ENDS are sexps in the variable `year' giving the daylight | |
e716fd62 | 339 | saving time start and end rules, in the form expected by |
3e03d7c7 | 340 | `calendar-daylight-savings-starts'. |
6bc457fe | 341 | DST-STARTS-TIME and DST-ENDS-TIME are integers giving the number of minutes |
e716fd62 | 342 | after midnight that daylight saving time starts and ends. |
3e03d7c7 | 343 | |
6bc457fe PE |
344 | If the local area does not use a seasonal time adjustment, STD-ZONE and |
345 | DST-ZONE are equal, and all the DST-* integer variables are 0. | |
3e03d7c7 JB |
346 | |
347 | Some operating systems cannot provide all this information to Emacs; in this | |
348 | case, `calendar-current-time-zone' returns a list containing nil for the data | |
349 | it can't find." | |
3d8b9024 AS |
350 | (or calendar-current-time-zone-cache |
351 | (setq calendar-current-time-zone-cache (calendar-dst-find-data)))) | |
3e03d7c7 | 352 | |
ec1ee609 GM |
353 | |
354 | ;; Following options should be set based on conditions when the code | |
355 | ;; is invoked, so are not suitable for dumping into loaddefs.el. They | |
356 | ;; default to US Eastern time if time zone info is not available. | |
3e03d7c7 JB |
357 | |
358 | (calendar-current-time-zone) | |
359 | ||
ec1ee609 | 360 | (defcustom calendar-time-zone (or (car calendar-current-time-zone-cache) -300) |
311cc551 | 361 | "Number of minutes difference between local standard time and UTC. |
ec1ee609 GM |
362 | For example, -300 for New York City, -480 for Los Angeles." |
363 | :type 'integer | |
364 | :group 'calendar-dst) | |
3e03d7c7 | 365 | |
ec1ee609 | 366 | (defcustom calendar-daylight-time-offset |
4b8683c7 | 367 | (or (cadr calendar-current-time-zone-cache) 60) |
ec1ee609 GM |
368 | "Number of minutes difference between daylight saving and standard time. |
369 | If the locale never uses daylight saving time, set this to 0." | |
370 | :type 'integer | |
371 | :group 'calendar-dst) | |
3e03d7c7 | 372 | |
ec1ee609 | 373 | (defcustom calendar-standard-time-zone-name |
4b8683c7 | 374 | (or (nth 2 calendar-current-time-zone-cache) "EST") |
ec1ee609 GM |
375 | "Abbreviated name of standard time zone at `calendar-location-name'. |
376 | For example, \"EST\" in New York City, \"PST\" for Los Angeles." | |
377 | :type 'string | |
378 | :group 'calendar-dst) | |
3e03d7c7 | 379 | |
ec1ee609 | 380 | (defcustom calendar-daylight-time-zone-name |
4b8683c7 | 381 | (or (nth 3 calendar-current-time-zone-cache) "EDT") |
ec1ee609 GM |
382 | "Abbreviated name of daylight saving time zone at `calendar-location-name'. |
383 | For example, \"EDT\" in New York City, \"PDT\" for Los Angeles." | |
384 | :type 'string | |
385 | :group 'calendar-dst) | |
386 | ||
387 | (defcustom calendar-daylight-savings-starts-time | |
4b8683c7 | 388 | (or (nth 6 calendar-current-time-zone-cache) 120) |
ec1ee609 GM |
389 | "Number of minutes after midnight that daylight saving time starts." |
390 | :type 'integer | |
391 | :group 'calendar-dst) | |
392 | ||
393 | (defcustom calendar-daylight-savings-ends-time | |
4b8683c7 | 394 | (or (nth 7 calendar-current-time-zone-cache) |
ec1ee609 GM |
395 | calendar-daylight-savings-starts-time) |
396 | "Number of minutes after midnight that daylight saving time ends." | |
397 | :type 'integer | |
398 | :group 'calendar-dst) | |
a1506d29 | 399 | |
cd72c399 GM |
400 | |
401 | (defun calendar-dst-starts (year) | |
e716fd62 | 402 | "Return the date of YEAR on which daylight saving time starts. |
cd72c399 GM |
403 | This function respects the value of `calendar-dst-check-each-year-flag'." |
404 | (or (let ((expr (if calendar-dst-check-each-year-flag | |
405 | (cadr (calendar-dst-find-startend year)) | |
406 | (nth 4 calendar-current-time-zone-cache)))) | |
407 | (if expr (eval expr))) | |
71ea27ee | 408 | ;; New US rules commencing 2007. ftp://elsie.nci.nih.gov/pub/. |
cd72c399 | 409 | (and (not (zerop calendar-daylight-time-offset)) |
ed589f9a | 410 | (calendar-nth-named-day 2 0 3 year)))) |
cd72c399 GM |
411 | |
412 | (defun calendar-dst-ends (year) | |
e716fd62 | 413 | "Return the date of YEAR on which daylight saving time ends. |
cd72c399 GM |
414 | This function respects the value of `calendar-dst-check-each-year-flag'." |
415 | (or (let ((expr (if calendar-dst-check-each-year-flag | |
416 | (nth 2 (calendar-dst-find-startend year)) | |
417 | (nth 5 calendar-current-time-zone-cache)))) | |
418 | (if expr (eval expr))) | |
71ea27ee | 419 | ;; New US rules commencing 2007. ftp://elsie.nci.nih.gov/pub/. |
cd72c399 | 420 | (and (not (zerop calendar-daylight-time-offset)) |
ed589f9a | 421 | (calendar-nth-named-day 1 0 11 year)))) |
cd72c399 | 422 | |
76db8823 | 423 | ;; used by calc, solar. |
ec230951 | 424 | (defun dst-in-effect (date) |
e716fd62 | 425 | "True if on absolute DATE daylight saving time is in effect. |
021edd45 | 426 | Fractional part of DATE is local standard time of day." |
e803eab7 | 427 | (let* ((year (calendar-extract-year |
ec230951 | 428 | (calendar-gregorian-from-absolute (floor date)))) |
021edd45 ER |
429 | (dst-starts-gregorian (eval calendar-daylight-savings-starts)) |
430 | (dst-ends-gregorian (eval calendar-daylight-savings-ends)) | |
431 | (dst-starts (and dst-starts-gregorian | |
ec230951 | 432 | (+ (calendar-absolute-from-gregorian |
021edd45 | 433 | dst-starts-gregorian) |
ec230951 ER |
434 | (/ calendar-daylight-savings-starts-time |
435 | 60.0 24.0)))) | |
021edd45 | 436 | (dst-ends (and dst-ends-gregorian |
ec230951 | 437 | (+ (calendar-absolute-from-gregorian |
021edd45 | 438 | dst-ends-gregorian) |
ec230951 ER |
439 | (/ (- calendar-daylight-savings-ends-time |
440 | calendar-daylight-time-offset) | |
441 | 60.0 24.0))))) | |
021edd45 ER |
442 | (and dst-starts dst-ends |
443 | (if (< dst-starts dst-ends) | |
444 | (and (<= dst-starts date) (< date dst-ends)) | |
445 | (or (<= dst-starts date) (< date dst-ends)))))) | |
ec230951 | 446 | |
76db8823 | 447 | ;; used by calc, lunar, solar. |
bc4f7f3d | 448 | (defun dst-adjust-time (date time) |
ec230951 ER |
449 | "Adjust, to account for dst on DATE, decimal fraction standard TIME. |
450 | Returns a list (date adj-time zone) where `date' and `adj-time' are the values | |
451 | adjusted for `zone'; here `date' is a list (month day year), `adj-time' is a | |
452 | decimal fraction time, and `zone' is a string. | |
453 | ||
e716fd62 | 454 | Conversion to daylight saving time is done according to |
ec230951 ER |
455 | `calendar-daylight-savings-starts', `calendar-daylight-savings-ends', |
456 | `calendar-daylight-savings-starts-time', | |
06e3b7ae | 457 | `calendar-daylight-savings-ends-time', and `calendar-daylight-time-offset'." |
ec230951 | 458 | (let* ((rounded-abs-date (+ (calendar-absolute-from-gregorian date) |
71ea27ee | 459 | (/ (round (* 60 time)) 60.0 24.0))) |
ec230951 | 460 | (dst (dst-in-effect rounded-abs-date)) |
71ea27ee GM |
461 | (time-zone (if dst |
462 | calendar-daylight-time-zone-name | |
463 | calendar-standard-time-zone-name)) | |
464 | (time (+ rounded-abs-date | |
ec230951 ER |
465 | (if dst (/ calendar-daylight-time-offset 24.0 60.0) 0)))) |
466 | (list (calendar-gregorian-from-absolute (truncate time)) | |
467 | (* 24.0 (- time (truncate time))) | |
468 | time-zone))) | |
469 | ||
3e03d7c7 JB |
470 | (provide 'cal-dst) |
471 | ||
472 | ;;; cal-dst.el ends here |