lisp/calendar/cal-china.el

   1 ;;; cal-chinese.el --- calendar functions for the Chinese calendar.
   2
   3 ;; Copyright (C) 1995 Free Software Foundation, Inc.
   4
   5 ;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
   6 ;; Keywords: calendar
   7 ;; Human-Keywords: Chinese calendar, calendar, holidays, diary
   8
   9 ;; This file is part of GNU Emacs.
  10
  11 ;; GNU Emacs is free software; you can redistribute it and/or modify
  12 ;; it under the terms of the GNU General Public License as published by
  13 ;; the Free Software Foundation; either version 2, or (at your option)
  14 ;; any later version.
  15
  16 ;; GNU Emacs is distributed in the hope that it will be useful,
  17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 ;; GNU General Public License for more details.
  20
  21 ;; You should have received a copy of the GNU General Public License
  22 ;; along with GNU Emacs; see the file COPYING.  If not, write to the
  23 ;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  24 ;; Boston, MA 02111-1307, USA.
  25
  26 ;;; Commentary:
  27
  28 ;; This collection of functions implements the features of calendar.el,
  29 ;; diary.el, and holidays.el that deal with the Chinese calendar.  The rules
  30 ;; used for the Chinese calendar are those of Baolin Liu (see L. E. Doggett's
  31 ;; article "Calendars" in the Explanatory Supplement to the Astronomical
  32 ;; Almanac, second edition, 1992) for the calendar as revised at the beginning
  33 ;; of the Qing dynasty in 1644.  The nature of the astronomical calculations
  34 ;; is such that precise calculations cannot be made without great expense in
  35 ;; time, so that the calendars produced may not agree perfectly with published
  36 ;; tables--but no two pairs of published tables agree perfectly either!  Liu's
  37 ;; rules produce a calendar for 2033 which is not accepted by all authorities.
  38 ;; The date of Chinese New Year is correct from 1644-2051.
  39
  40 ;; Comments, corrections, and improvements should be sent to
  41 ;;  Edward M. Reingold               Department of Computer Science
  42 ;;  (217) 333-6733                   University of Illinois at Urbana-Champaign
  43 ;;  reingold@cs.uiuc.edu             1304 West Springfield Avenue
  44 ;;                                   Urbana, Illinois 61801
  45
  46 ;;; Code:
  47
  48 (require 'lunar)
  49
  50 (defvar chinese-calendar-celestial-stem
  51   ["Jia" "Yi" "Bing" "Ding" "Wu" "Ji" "Geng" "Xin" "Ren" "Gui"])
  52
  53 (defvar chinese-calendar-terrestrial-branch
  54   ["Zi" "Chou" "Yin" "Mao" "Chen" "Si" "Wu" "Wei" "Shen" "You" "Xu" "Hai"])
  55
  56 (defvar chinese-calendar-time-zone
  57   '(if (< year 1928)
  58        (+ 465 (/ 40.0 60.0))
  59      480)
  60   "*Number of minutes difference between local standard time for Chinese
  61 calendar and Coordinated Universal (Greenwich) Time.  Default is for Beijing.
  62 This is an expression in `year' since it changed at 1928-01-01 00:00:00 from
  63 UT+7:45:40 to UT+8.")
  64
  65 (defvar chinese-calendar-location-name "Beijing"
  66   "*Name of location used for calculation of Chinese calendar.")
  67
  68 (defvar chinese-calendar-daylight-time-offset 0
  69 ; The correct value is as follows, but the Chinese calendrical
  70 ; authorities do NOT use DST in determining astronomical events:
  71 ;  60
  72   "*Number of minutes difference between daylight savings and standard time
  73 for Chinese calendar.  Default is for no daylight savings time.")
  74
  75 (defvar chinese-calendar-standard-time-zone-name
  76   '(if (< year 1928)
  77        "PMT"
  78      "CST")
  79   "*Abbreviated name of standard time zone used for Chinese calendar.")
  80
  81 (defvar chinese-calendar-daylight-time-zone-name "CDT"
  82   "*Abbreviated name of daylight-savings time zone used for Chinese calendar.")
  83
  84 (defvar chinese-calendar-daylight-savings-starts nil
  85 ; The correct value is as follows, but the Chinese calendrical
  86 ; authorities do NOT use DST in determining astronomical events:
  87 ;  '(cond ((< 1986 year) (calendar-nth-named-day 1 0 4 year 10))
  88 ;         ((= 1986 year) '(5 4 1986))
  89 ;         (t nil))
  90   "*Sexp giving the date on which daylight savings time starts for Chinese
  91 calendar.  Default is for no daylight savings time.  See documentation of
  92 `calendar-daylight-savings-starts'.")
  93
  94 (defvar chinese-calendar-daylight-savings-ends nil
  95 ; The correct value is as follows, but the Chinese calendrical
  96 ; authorities do NOT use DST in determining astronomical events:
  97 ;  '(if (<= 1986 year) (calendar-nth-named-day 1 0 9 year 11))
  98   "*Sexp giving the date on which daylight savings time ends for Chinese
  99 calendar.  Default is for no daylight savings time.  See documentation of
 100 `calendar-daylight-savings-ends'.")
 101
 102 (defvar chinese-calendar-daylight-savings-starts-time 0
 103   "*Number of minutes after midnight that daylight savings time starts for
 104 Chinese calendar.  Default is for no daylight savings time.")
 105
 106 (defvar chinese-calendar-daylight-savings-ends-time 0
 107   "*Number of minutes after midnight that daylight savings time ends for
 108 Chinese calendar.  Default is for no daylight savings time.")
 109
 110 (defun chinese-zodiac-sign-on-or-after (d)
 111   "Absolute date of first new Zodiac sign on or after absolute date d.
 112 The Zodiac signs begin when the sun's longitude is a multiple of 30 degrees."
 113  (let* ((year (extract-calendar-year
 114                 (calendar-gregorian-from-absolute d)))
 115          (calendar-time-zone (eval chinese-calendar-time-zone))
 116          (calendar-daylight-time-offset
 117           chinese-calendar-daylight-time-offset)
 118          (calendar-standard-time-zone-name
 119           chinese-calendar-standard-time-zone-name)
 120          (calendar-daylight-time-zone-name
 121           chinese-calendar-daylight-time-zone-name)
 122          (calendar-calendar-daylight-savings-starts
 123           chinese-calendar-daylight-savings-starts)
 124          (calendar-daylight-savings-ends
 125           chinese-calendar-daylight-savings-ends)
 126          (calendar-daylight-savings-starts-time
 127           chinese-calendar-daylight-savings-starts-time)
 128          (calendar-daylight-savings-ends-time
 129           chinese-calendar-daylight-savings-ends-time))
 130    (floor
 131     (calendar-absolute-from-astro
 132      (solar-date-next-longitude
 133       (calendar-astro-from-absolute d)
 134       30)))))
 135
 136 (defun chinese-new-moon-on-or-after (d)
 137   "Absolute date of first new moon on or after absolute date d."
 138   (let* ((year (extract-calendar-year
 139                 (calendar-gregorian-from-absolute d)))
 140          (calendar-time-zone (eval chinese-calendar-time-zone))
 141          (calendar-daylight-time-offset
 142           chinese-calendar-daylight-time-offset)
 143          (calendar-standard-time-zone-name
 144           chinese-calendar-standard-time-zone-name)
 145          (calendar-daylight-time-zone-name
 146           chinese-calendar-daylight-time-zone-name)
 147          (calendar-calendar-daylight-savings-starts
 148           chinese-calendar-daylight-savings-starts)
 149          (calendar-daylight-savings-ends
 150           chinese-calendar-daylight-savings-ends)
 151          (calendar-daylight-savings-starts-time
 152           chinese-calendar-daylight-savings-starts-time)
 153          (calendar-daylight-savings-ends-time
 154           chinese-calendar-daylight-savings-ends-time))
 155     (floor
 156      (calendar-absolute-from-astro
 157       (lunar-new-moon-on-or-after
 158        (calendar-astro-from-absolute d))))))
 159
 160 (defvar chinese-year-cache
 161   '((1989 (12 726110) (1 726139) (2 726169) (3 726198) (4 726227) (5 726257)
 162           (6 726286) (7 726316) (8 726345) (9 726375) (10 726404) (11 726434))
 163     (1990 (12 726464) (1 726494) (2 726523) (3 726553) (4 726582) (5 726611)
 164           (5.5 726641) (6 726670) (7 726699) (8 726729) (9 726758) (10 726788)
 165           (11 726818))
 166     (1991 (12 726848) (1 726878) (2 726907) (3 726937) (4 726966) (5 726995)
 167           (6 727025) (7 727054) (8 727083) (9 727113) (10 727142) (11 727172))
 168     (1992 (12 727202) (1 727232) (2 727261) (3 727291) (4 727321) (5 727350)
 169           (6 727379) (7 727409) (8 727438) (9 727467) (10 727497) (11 727526))
 170     (1993 (12 727556) (1 727586) (2 727615) (3 727645) (3.5 727675) (4 727704)
 171           (5 727734) (6 727763) (7 727793) (8 727822) (9 727851) (10 727881)
 172           (11 727910))
 173     (1994 (12 727940) (1 727969) (2 727999) (3 728029) (4 728059) (5 728088)
 174           (6 728118) (7 728147) (8 728177) (9 728206) (10 728235) (11 728265))
 175     (1995 (12 728294) (1 728324) (2 728353) (3 728383) (4 728413) (5 728442)
 176           (6 728472) (7 728501) (8 728531) (8.5 728561) (9 728590) (10 728619)
 177           (11 728649))
 178     (1996 (12 728678) (1 728708) (2 728737) (3 728767) (4 728796) (5 728826)
 179           (6 728856) (7 728885) (8 728915) (9 728944) (10 728974) (11 729004))
 180     (1997 (12 729033) (1 729062) (2 729092) (3 729121) (4 729151) (5 729180)
 181           (6 729210) (7 729239) (8 729269) (9 729299) (10 729328) (11 729358))
 182     (1998 (12 729388) (1 729417) (2 729447) (3 729476) (4 729505) (5 729535)
 183           (5.5 729564) (6 729593) (7 729623) (8 729653) (9 729682) (10 729712)
 184           (11 729742))
 185     (1999 (12 729771) (1 729801) (2 729831) (3 729860) (4 729889) (5 729919)
 186           (6 729948) (7 729977) (8 730007) (9 730036) (10 730066) (11 730096))
 187     (2000 (12 730126) (1 730155) (2 730185) (3 730215) (4 730244) (5 730273)
 188           (6 730303) (7 730332) (8 730361) (9 730391) (10 730420) (11 730450)))
 189   "An assoc list of Chinese year structures as determined by `chinese-year'.
 190
 191 Values are computed as needed, but to save time, the initial value consists
 192 of the precomputed years 1989-2000.  The code works just as well with this
 193 set to nil initially (which is how the value for 1989-2000 was computed).")
 194
 195 (defun chinese-year (y)
 196   "The structure of the Chinese year for Gregorian year Y.
 197 The result is a list of pairs (i d), where month i begins on absolute date d,
 198 of the Chinese months from the Chinese month following the solstice in
 199 Gregorian year Y-1 to the Chinese month of the solstice of Gregorian year Y.
 200
 201 The list is cached for further use."
 202   (let ((list (cdr (assoc y chinese-year-cache))))
 203     (if (not list)
 204         (progn
 205           (setq list (compute-chinese-year y))
 206           (setq chinese-year-cache
 207                 (append chinese-year-cache (list (cons y list))))))
 208     list))
 209
 210 (defun number-chinese-months (list start)
 211   "Assign month numbers to the lunar months in LIST, starting with START.
 212 Numbers are assigned sequentially, START, START+1, ..., 11, with half
 213 numbers used for leap months.
 214
 215 First month of list will never be a leap month, nor will the last."
 216   (if list
 217       (if (zerop (- 12 start (length list)))
 218           ;; List is too short for a leap month
 219           (cons (list start (car list))
 220                 (number-chinese-months (cdr list) (1+ start)))
 221         (cons
 222          ;; First month
 223          (list start (car list))
 224          ;; Remaining months
 225          (if (and (cdr (cdr list));; at least two more months...
 226                   (<= (car (cdr (cdr list)))
 227                       (chinese-zodiac-sign-on-or-after (car (cdr list)))))
 228              ;; Next month is a leap month
 229              (cons (list (+ start 0.5) (car (cdr list)))
 230                    (number-chinese-months (cdr (cdr list)) (1+ start)))
 231            ;; Next month is not a leap month
 232            (number-chinese-months (cdr list) (1+ start)))))))
 233
 234 (defun chinese-month-list (start end)
 235   "List of starting dates of Chinese months from START to END."
 236   (if (<= start end)
 237       (let ((new-moon (chinese-new-moon-on-or-after start)))
 238         (if (<= new-moon end)
 239             (cons new-moon
 240                   (chinese-month-list (1+ new-moon) end))))))
 241
 242 (defun compute-chinese-year (y)
 243   "Compute the structure of the Chinese year for Gregorian year Y.
 244 The result is a list of pairs (i d), where month i begins on absolute date d,
 245 of the Chinese months from the Chinese month following the solstice in
 246 Gregorian year Y-1 to the Chinese month of the solstice of Gregorian year Y."
 247   (let* ((next-solstice (chinese-zodiac-sign-on-or-after
 248                          (calendar-absolute-from-gregorian
 249                           (list 12 15 y))))
 250          (list (chinese-month-list (1+ (chinese-zodiac-sign-on-or-after
 251                                         (calendar-absolute-from-gregorian
 252                                          (list 12 15 (1- y)))))
 253                                    next-solstice))
 254          (next-sign (chinese-zodiac-sign-on-or-after (car list))))
 255     (if (= (length list) 12)
 256         ;; No room for a leap month, just number them 12, 1, 2, ..., 11
 257         (cons (list 12 (car list))
 258               (number-chinese-months (cdr list) 1))
 259       ;; Now we can assign numbers to the list for y
 260       ;; The first month or two are special
 261       (if (or (> (car list) next-sign) (>= next-sign (car (cdr list))))
 262           ;; First month on list is a leap month, second is not
 263           (append (list (list 11.5 (car list))
 264                         (list 12 (car (cdr list))))
 265                   (number-chinese-months (cdr (cdr list)) 1))
 266         ;; First month on list is not a leap month
 267         (append (list (list 12 (car list)))
 268                 (if (>= (chinese-zodiac-sign-on-or-after (car (cdr list)))
 269                         (car (cdr (cdr list))))
 270                     ;; Second month on list is a leap month
 271                     (cons (list 12.5 (car (cdr list)))
 272                           (number-chinese-months (cdr (cdr list)) 1))
 273                   ;; Second month on list is not a leap month
 274                   (number-chinese-months (cdr list) 1)))))))
 275
 276 (defun calendar-absolute-from-chinese (date)
 277   "The number of days elapsed between the Gregorian date 12/31/1 BC and DATE.
 278 The Gregorian date Sunday, December 31, 1 BC is imaginary."
 279   (let* ((cycle (car date))
 280          (year (car (cdr date)))
 281          (month (car (cdr (cdr date))))
 282          (day (car (cdr (cdr (cdr date)))))
 283          (g-year (+ (* (1- cycle) 60);; years in prior cycles
 284                     (1- year)        ;; prior years this cycle
 285                     -2636)))         ;; years before absolute date 0
 286     (+ (1- day);; prior days this month
 287        (car
 288         (cdr    ;; absolute date of start of this month
 289          (assoc month (append (memq (assoc 1 (chinese-year g-year))
 290                                     (chinese-year g-year))
 291                               (chinese-year (1+ g-year)))))))))
 292
 293 (defun calendar-chinese-from-absolute (date)
 294   "Compute Chinese date (cycle year month day) corresponding to absolute DATE.
 295 The absolute date is the number of days elapsed since the (imaginary)
 296 Gregorian date Sunday, December 31, 1 BC."
 297   (let* ((g-year (extract-calendar-year
 298                   (calendar-gregorian-from-absolute date)))
 299          (c-year (+ g-year 2695))
 300          (list (append (chinese-year (1- g-year))
 301                        (chinese-year g-year)
 302                        (chinese-year (1+ g-year)))))
 303     (while (<= (car (cdr (car (cdr list)))) date)
 304       ;; the first month on the list is in Chinese year c-year
 305       ;; date is on or after start of second month on list...
 306       (if (= 1 (car (car (cdr list))))
 307           ;; second month on list is a new Chinese year
 308           (setq c-year (1+ c-year)))
 309       ;; ...so first month on list is of no interest
 310       (setq list (cdr list)))
 311     (list (/ (1- c-year) 60)
 312           (calendar-mod c-year 60)
 313           (car (car list))
 314           (1+ (- date (car (cdr (car list))))))))
 315
 316 (defun holiday-chinese-new-year ()
 317   "Date of Chinese New Year."
 318   (let ((m displayed-month)
 319         (y displayed-year))
 320     (increment-calendar-month m y 1)
 321     (if (< m 5)
 322         (let ((chinese-new-year
 323                (calendar-gregorian-from-absolute
 324                 (car (cdr (assoc 1 (chinese-year y)))))))
 325           (if (calendar-date-is-visible-p chinese-new-year)
 326           (list
 327            (list chinese-new-year
 328                  (format "Chinese New Year (%s)"
 329                          (calendar-chinese-sexagesimal-name (+ y 57))))))))))
 330
 331 (defun calendar-chinese-date-string (&optional date)
 332   "String of Chinese date of Gregorian DATE.
 333 Defaults to today's date if DATE is not given."
 334   (let* ((a-date (calendar-absolute-from-gregorian
 335                   (or date (calendar-current-date))))
 336          (c-date (calendar-chinese-from-absolute a-date))
 337          (cycle (car c-date))
 338          (year (car (cdr c-date)))
 339          (month (car (cdr (cdr c-date))))
 340          (day (car (cdr (cdr (cdr c-date)))))
 341          (this-month (calendar-absolute-from-chinese
 342                       (list cycle year month 1)))
 343          (next-month (calendar-absolute-from-chinese
 344                       (list (if (= year 60) (1+ cycle) cycle)
 345                             (if (= (floor month) 12) (1+ year) year)
 346                             (calendar-mod (1+ (floor month)) 12)
 347                             1)))
 348          (m-cycle (% (+ (* year 5) (floor month)) 60)))
 349     (format "Cycle %s, year %s (%s), %smonth %s%s, day %s (%s)"
 350             cycle
 351             year (calendar-chinese-sexagesimal-name year)
 352             (if (not (integerp month))
 353                 "second "
 354               (if (< 30 (- next-month this-month))
 355                   "first "
 356                 ""))
 357             (floor month)
 358             (if (integerp month)
 359                 (format " (%s)" (calendar-chinese-sexagesimal-name
 360                                  (+ (* 5 year) month 44)))
 361               "")
 362             day (calendar-chinese-sexagesimal-name (+ a-date 15)))))
 363
 364 (defun calendar-chinese-sexagesimal-name (n)
 365   "The N-th name of the Chinese sexagesimal cycle.
 366 N congruent to 1 gives the first name, N congruent to 2 gives the second name,
 367 ..., N congruent to 60 gives the sixtieth name."
 368   (format "%s-%s"
 369           (aref chinese-calendar-celestial-stem (% (1- n) 10))
 370           (aref chinese-calendar-terrestrial-branch (% (1- n) 12))))
 371
 372 (defun calendar-print-chinese-date ()
 373   "Show the Chinese date equivalents of date."
 374   (interactive)
 375   (message "Computing Chinese date...")
 376   (message "Chinese date: %s"
 377            (calendar-chinese-date-string (calendar-cursor-to-date t))))
 378
 379 (defun calendar-goto-chinese-date (date &optional noecho)
 380   "Move cursor to Chinese date DATE.
 381 Echo Chinese date unless NOECHO is t."
 382   (interactive
 383    (let* ((c (calendar-chinese-from-absolute
 384               (calendar-absolute-from-gregorian
 385                (calendar-current-date))))
 386           (cycle (calendar-read
 387                   "Chinese calendar cycle number (>44): "
 388                   '(lambda (x) (> x 44))
 389                   (int-to-string (car c))))
 390           (year (calendar-read
 391                  "Year in Chinese cycle (1..60): "
 392                  '(lambda (x) (and (<= 1 x) (<= x 60)))
 393                  (int-to-string (car (cdr c)))))
 394           (month-list (make-chinese-month-assoc-list
 395                        (chinese-months cycle year)))
 396           (month (cdr (assoc
 397                        (completing-read "Chinese calendar month: "
 398                                         month-list nil t)
 399                        month-list)))
 400           (last (if (= month
 401                        (car (cdr (cdr
 402                                   (calendar-chinese-from-absolute
 403                                    (+ 29
 404                                       (calendar-absolute-from-chinese
 405                                        (list cycle year month 1))))))))
 406                     30
 407                   29))
 408           (day (calendar-read
 409                 (format "Chinese calendar day (1-%d): " last)
 410                 '(lambda (x) (and (<= 1 x) (<= x last))))))
 411      (list (list cycle year month day))))
 412   (calendar-goto-date (calendar-gregorian-from-absolute
 413                        (calendar-absolute-from-chinese date)))
 414   (or noecho (calendar-print-chinese-date)))
 415
 416 (defun chinese-months (c y)
 417   "A list of the months in cycle C, year Y of the Chinese calendar."
 418   (let* ((l (memq 1 (append
 419                      (mapcar '(lambda (x)
 420                                 (car x))
 421                              (chinese-year (extract-calendar-year
 422                                             (calendar-gregorian-from-absolute
 423                                              (calendar-absolute-from-chinese
 424                                               (list c y 1 1))))))
 425                      (mapcar '(lambda (x)
 426                                 (if (> (car x) 11) (car x)))
 427                              (chinese-year (extract-calendar-year
 428                                             (calendar-gregorian-from-absolute
 429                                              (calendar-absolute-from-chinese
 430                                               (list (if (= y 60) (1+ c) c)
 431                                                     (if (= y 60) 1 y)
 432                                                     1 1))))))))))
 433     l))
 434
 435 (defun make-chinese-month-assoc-list (l)
 436   "Make list of months L into an assoc list."
 437   (if (and l (car l))
 438       (if (and (cdr l) (car (cdr l)))
 439           (if (= (car l) (floor (car (cdr l))))
 440               (append
 441                (list (cons (format "%s (first)" (car l)) (car l))
 442                      (cons (format "%s (second)" (car l)) (car (cdr l))))
 443                (make-chinese-month-assoc-list (cdr (cdr l))))
 444             (append
 445              (list (cons (int-to-string (car l)) (car l)))
 446              (make-chinese-month-assoc-list (cdr l))))
 447         (list (cons (int-to-string (car l)) (car l))))))
 448
 449 (defun diary-chinese-date ()
 450   "Chinese calendar equivalent of date diary entry."
 451   (format "Chinese date: %s" (calendar-chinese-date-string date)))
 452
 453 (provide 'cal-chinese)
 454
 455 ;;; cal-chinese ends here