1 ;;; cal-julian.el --- calendar functions for the Julian calendar
3 ;; Copyright (C) 1995, 1997 Free Software Foundation, Inc.
5 ;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
7 ;; Human-Keywords: Julian calendar, Julian day number, calendar, diary
9 ;; This file is part of GNU Emacs.
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)
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.
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.
28 ;; This collection of functions implements the features of calendar.el and
29 ;; diary.el that deal with the Julian calendar.
31 ;; Technical details of all the calendrical calculations can be found in
32 ;; ``Calendrical Calculations'' by Nachum Dershowitz and Edward M. Reingold,
33 ;; Cambridge University Press (1997).
35 ;; Comments, corrections, and improvements should be sent to
36 ;; Edward M. Reingold Department of Computer Science
37 ;; (217) 333-6733 University of Illinois at Urbana-Champaign
38 ;; reingold@cs.uiuc.edu 1304 West Springfield Avenue
39 ;; Urbana, Illinois 61801
43 (defvar displayed-month
)
44 (defvar displayed-year
)
48 (defun calendar-julian-from-absolute (date)
49 "Compute the Julian (month day year) corresponding to the absolute DATE.
50 The absolute date is the number of days elapsed since the (imaginary)
51 Gregorian date Sunday, December 31, 1 BC."
52 (let* ((approx (/ (+ date
2) 366));; Approximation from below.
53 (year ;; Search forward from the approximation.
55 (calendar-sum y approx
56 (>= date
(calendar-absolute-from-julian (list 1 1 (1+ y
))))
58 (month ;; Search forward from January.
61 (calendar-absolute-from-julian
63 (if (and (= m
2) (= (% year
4) 0))
65 (aref [31 28 31 30 31 30 31 31 30 31 30 31]
69 (day ;; Calculate the day by subtraction.
70 (- date
(1- (calendar-absolute-from-julian (list month
1 year
))))))
71 (list month day year
)))
73 (defun calendar-absolute-from-julian (date)
74 "The number of days elapsed between the Gregorian date 12/31/1 BC and DATE.
75 The Gregorian date Sunday, December 31, 1 BC is imaginary."
76 (let ((month (extract-calendar-month date
))
77 (day (extract-calendar-day date
))
78 (year (extract-calendar-year date
)))
79 (+ (calendar-day-number date
)
80 (if (and (= (% year
100) 0)
83 1 0);; Correct for Julian but not Gregorian leap year.
88 (defun calendar-julian-date-string (&optional date
)
89 "String of Julian date of Gregorian DATE.
90 Defaults to today's date if DATE is not given.
91 Driven by the variable `calendar-date-display-form'."
93 (calendar-julian-from-absolute
94 (calendar-absolute-from-gregorian
95 (or date
(calendar-current-date))))
98 (defun calendar-print-julian-date ()
99 "Show the Julian calendar equivalent of the date under the cursor."
101 (message "Julian date: %s"
102 (calendar-julian-date-string (calendar-cursor-to-date t
))))
104 (defun calendar-goto-julian-date (date &optional noecho
)
105 "Move cursor to Julian DATE; echo Julian date unless NOECHO is t."
107 (let* ((today (calendar-current-date))
109 "Julian calendar year (>0): "
110 '(lambda (x) (> x
0))
112 (extract-calendar-year
113 (calendar-julian-from-absolute
114 (calendar-absolute-from-gregorian
116 (month-array calendar-month-name-array
)
117 (completion-ignore-case t
)
118 (month (cdr (assoc-ignore-case
120 "Julian calendar month name: "
121 (mapcar 'list
(append month-array nil
))
123 (calendar-make-alist month-array
1))))
125 (if (and (zerop (% year
4)) (= month
2))
127 (aref [31 28 31 30 31 30 31 31 30 31 30 31] (1- month
))))
129 (format "Julian calendar day (%d-%d): "
130 (if (and (= year
1) (= month
1)) 3 1) last
)
132 (and (< (if (and (= year
1) (= month
1)) 2 0) x
)
134 (list (list month day year
))))
135 (calendar-goto-date (calendar-gregorian-from-absolute
136 (calendar-absolute-from-julian date
)))
137 (or noecho
(calendar-print-julian-date)))
139 (defun holiday-julian (month day string
)
140 "Holiday on MONTH, DAY (Julian) called STRING.
141 If MONTH, DAY (Julian) is visible, the value returned is corresponding
142 Gregorian date in the form of the list (((month day year) STRING)). Returns
143 nil if it is not visible in the current calendar window."
144 (let ((m1 displayed-month
)
149 (increment-calendar-month m1 y1 -
1)
150 (increment-calendar-month m2 y2
1)
151 (let* ((start-date (calendar-absolute-from-gregorian
153 (end-date (calendar-absolute-from-gregorian
154 (list m2
(calendar-last-day-of-month m2 y2
) y2
)))
155 (julian-start (calendar-julian-from-absolute start-date
))
156 (julian-end (calendar-julian-from-absolute end-date
))
157 (julian-y1 (extract-calendar-year julian-start
))
158 (julian-y2 (extract-calendar-year julian-end
)))
159 (setq year
(if (< 10 month
) julian-y1 julian-y2
))
160 (let ((date (calendar-gregorian-from-absolute
161 (calendar-absolute-from-julian
162 (list month day year
)))))
163 (if (calendar-date-is-visible-p date
)
164 (list (list date string
)))))))
166 (defun diary-julian-date ()
167 "Julian calendar equivalent of date diary entry."
168 (format "Julian date: %s" (calendar-julian-date-string date
)))
170 (defun calendar-absolute-from-astro (d)
171 "Absolute date of astronomical (Julian) day number D."
174 (defun calendar-astro-from-absolute (d)
175 "Astronomical (Julian) day number of absolute date D."
178 (defun calendar-astro-date-string (&optional date
)
179 "String of astronomical (Julian) day number after noon UTC of Gregorian DATE.
180 Defaults to today's date if DATE is not given."
183 (calendar-astro-from-absolute
184 (calendar-absolute-from-gregorian
185 (or date
(calendar-current-date)))))))
187 (defun calendar-print-astro-day-number ()
188 "Show astronomical (Julian) day number after noon UTC on date shown by cursor."
191 "Astronomical (Julian) day number (at noon UTC): %s.0"
192 (calendar-astro-date-string (calendar-cursor-to-date t
))))
194 (defun calendar-goto-astro-day-number (daynumber &optional noecho
)
195 "Move cursor to astronomical (Julian) DAYNUMBER.
196 Echo astronomical (Julian) day number unless NOECHO is t."
197 (interactive (list (calendar-read
198 "Astronomical (Julian) day number (>1721425): "
199 '(lambda (x) (> x
1721425)))))
201 (calendar-gregorian-from-absolute
203 (calendar-absolute-from-astro daynumber
))))
204 (or noecho
(calendar-print-astro-day-number)))
206 (defun diary-astro-day-number ()
207 "Astronomical (Julian) day number diary entry."
208 (format "Astronomical (Julian) day number at noon UTC: %s.0"
209 (calendar-astro-date-string date
)))
211 (provide 'cal-julian
)
213 ;;; arch-tag: 0520acdd-1c60-4188-9aa8-9b8c24d856ae
214 ;;; cal-julian.el ends here