1 ;;; cal-coptic.el --- calendar functions for the Coptic/Ethiopic calendars
3 ;; Copyright (C) 1995, 1997 Free Software Foundation, Inc.
5 ;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
7 ;; Human-Keywords: Coptic calendar, Ethiopic calendar, 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., 51 Franklin Street, Fifth Floor,
24 ;; Boston, MA 02110-1301, USA.
28 ;; This collection of functions implements the features of calendar.el and
29 ;; diary.el that deal with the Coptic and Ethiopic calendars.
31 ;; Technical details of all the calendrical calculations can be found in
32 ;; ``Calendrical Calculations: The Millennium Edition'' by Edward M. Reingold
33 ;; and Nachum Dershowitz, Cambridge University Press (2001).
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
47 (defvar coptic-calendar-month-name-array
48 ["Tut" "Babah" "Hatur" "Kiyahk" "Tubah" "Amshir" "Baramhat" "Barmundah"
49 "Bashans" "Baunah" "Abib" "Misra" "al-Nasi"])
51 (defvar coptic-calendar-epoch
(calendar-absolute-from-julian '(8 29 284))
52 "Absolute date of start of Coptic calendar = August 29, 284 A.D. (Julian).")
54 (defvar coptic-name
"Coptic")
56 (defun coptic-calendar-leap-year-p (year)
57 "True if YEAR is a leap year on the Coptic calendar."
58 (zerop (mod (1+ year
) 4)))
60 (defun coptic-calendar-last-day-of-month (month year
)
61 "Return last day of MONTH, YEAR on the Coptic calendar.
62 The 13th month is not really a month, but the 5 (6 in leap years) day period of
63 Nisi (Kebus) at the end of the year."
66 (if (coptic-calendar-leap-year-p year
)
70 (defun calendar-absolute-from-coptic (date)
71 "Compute absolute date from Coptic date DATE.
72 The absolute date is the number of days elapsed since the (imaginary)
73 Gregorian date Sunday, December 31, 1 BC."
74 (let ((month (extract-calendar-month date
))
75 (day (extract-calendar-day date
))
76 (year (extract-calendar-year date
)))
77 (+ (1- coptic-calendar-epoch
);; Days before start of calendar
78 (* 365 (1- year
)) ;; Days in prior years
79 (/ year
4) ;; Leap days in prior years
80 (* 30 (1- month
)) ;; Days in prior months this year
81 day
))) ;; Days so far this month
84 (defun calendar-coptic-from-absolute (date)
85 "Compute the Coptic equivalent for absolute date DATE.
86 The result is a list of the form (MONTH DAY YEAR).
87 The absolute date is the number of days elapsed since the imaginary
88 Gregorian date Sunday, December 31, 1 BC."
89 (if (< date coptic-calendar-epoch
)
90 (list 0 0 0);; pre-Coptic date
91 (let* ((approx (/ (- date coptic-calendar-epoch
)
92 366)) ;; Approximation from below.
93 (year ;; Search forward from the approximation.
95 (calendar-sum y approx
96 (>= date
(calendar-absolute-from-coptic (list 1 1 (1+ y
))))
98 (month ;; Search forward from Tot.
101 (calendar-absolute-from-coptic
103 (coptic-calendar-last-day-of-month m year
)
106 (day ;; Calculate the day by subtraction.
108 (1- (calendar-absolute-from-coptic (list month
1 year
))))))
109 (list month day year
))))
111 (defun calendar-coptic-date-string (&optional date
)
112 "String of Coptic date of Gregorian DATE.
113 Returns the empty string if DATE is pre-Coptic calendar.
114 Defaults to today's date if DATE is not given."
115 (let* ((coptic-date (calendar-coptic-from-absolute
116 (calendar-absolute-from-gregorian
117 (or date
(calendar-current-date)))))
118 (y (extract-calendar-year coptic-date
))
119 (m (extract-calendar-month coptic-date
)))
122 (let ((monthname (aref coptic-calendar-month-name-array
(1- m
)))
123 (day (int-to-string (extract-calendar-day coptic-date
)))
125 (month (int-to-string m
))
126 (year (int-to-string y
)))
127 (mapconcat 'eval calendar-date-display-form
"")))))
129 (defun calendar-print-coptic-date ()
130 "Show the Coptic calendar equivalent of the selected date."
132 (let ((f (calendar-coptic-date-string (calendar-cursor-to-date t
))))
133 (if (string-equal f
"")
134 (message "Date is pre-%s calendar" coptic-name
)
135 (message "%s date: %s" coptic-name f
))))
137 (defun calendar-goto-coptic-date (date &optional noecho
)
138 "Move cursor to Coptic date DATE.
139 Echo Coptic date unless NOECHO is t."
140 (interactive (coptic-prompt-for-date))
141 (calendar-goto-date (calendar-gregorian-from-absolute
142 (calendar-absolute-from-coptic date
)))
143 (or noecho
(calendar-print-coptic-date)))
145 (defun coptic-prompt-for-date ()
146 "Ask for a Coptic date."
147 (let* ((today (calendar-current-date))
149 (format "%s calendar year (>0): " coptic-name
)
150 '(lambda (x) (> x
0))
152 (extract-calendar-year
153 (calendar-coptic-from-absolute
154 (calendar-absolute-from-gregorian today
))))))
155 (completion-ignore-case t
)
156 (month (cdr (assoc-string
158 (format "%s calendar month name: " coptic-name
)
160 (append coptic-calendar-month-name-array nil
))
162 (calendar-make-alist coptic-calendar-month-name-array
164 (last (coptic-calendar-last-day-of-month month year
))
166 (format "%s calendar day (1-%d): " coptic-name last
)
167 '(lambda (x) (and (< 0 x
) (<= x last
))))))
168 (list (list month day year
))))
170 (defun diary-coptic-date ()
171 "Coptic calendar equivalent of date diary entry."
172 (let ((f (calendar-coptic-date-string date
)))
173 (if (string-equal f
"")
174 (format "Date is pre-%s calendar" coptic-name
)
175 (format "%s date: %s" coptic-name f
))))
177 (defconst ethiopic-calendar-month-name-array
178 ["Maskaram" "Teqemt" "Khedar" "Takhsas" "Ter" "Yakatit" "Magabit" "Miyazya"
179 "Genbot" "Sane" "Hamle" "Nahas" "Paguem"])
181 (defconst ethiopic-calendar-epoch
2796
182 "Absolute date of start of Ethiopic calendar = August 29, 8 C.E. (Julian).")
184 (defconst ethiopic-name
"Ethiopic")
186 (defun calendar-absolute-from-ethiopic (date)
187 "Compute absolute date from Ethiopic date DATE.
188 The absolute date is the number of days elapsed since the (imaginary)
189 Gregorian date Sunday, December 31, 1 BC."
190 (let ((coptic-calendar-epoch ethiopic-calendar-epoch
))
191 (calendar-absolute-from-coptic date
)))
193 (defun calendar-ethiopic-from-absolute (date)
194 "Compute the Ethiopic equivalent for absolute date DATE.
195 The result is a list of the form (MONTH DAY YEAR).
196 The absolute date is the number of days elapsed since the imaginary
197 Gregorian date Sunday, December 31, 1 BC."
198 (let ((coptic-calendar-epoch ethiopic-calendar-epoch
))
199 (calendar-coptic-from-absolute date
)))
201 (defun calendar-ethiopic-date-string (&optional date
)
202 "String of Ethiopic date of Gregorian DATE.
203 Returns the empty string if DATE is pre-Ethiopic calendar.
204 Defaults to today's date if DATE is not given."
205 (let ((coptic-calendar-epoch ethiopic-calendar-epoch
)
206 (coptic-name ethiopic-name
)
207 (coptic-calendar-month-name-array ethiopic-calendar-month-name-array
))
208 (calendar-coptic-date-string date
)))
210 (defun calendar-print-ethiopic-date ()
211 "Show the Ethiopic calendar equivalent of the selected date."
213 (let ((coptic-calendar-epoch ethiopic-calendar-epoch
)
214 (coptic-name ethiopic-name
)
215 (coptic-calendar-month-name-array ethiopic-calendar-month-name-array
))
216 (call-interactively 'calendar-print-coptic-date
)))
218 (defun calendar-goto-ethiopic-date (date &optional noecho
)
219 "Move cursor to Ethiopic date DATE.
220 Echo Ethiopic date unless NOECHO is t."
222 (let ((coptic-calendar-epoch ethiopic-calendar-epoch
)
223 (coptic-name ethiopic-name
)
224 (coptic-calendar-month-name-array ethiopic-calendar-month-name-array
))
225 (coptic-prompt-for-date)))
226 (calendar-goto-date (calendar-gregorian-from-absolute
227 (calendar-absolute-from-ethiopic date
)))
228 (or noecho
(calendar-print-ethiopic-date)))
230 (defun diary-ethiopic-date ()
231 "Ethiopic calendar equivalent of date diary entry."
232 (let ((coptic-calendar-epoch ethiopic-calendar-epoch
)
233 (coptic-name ethiopic-name
)
234 (coptic-calendar-month-name-array ethiopic-calendar-month-name-array
))
235 (diary-coptic-date)))
237 (provide 'cal-coptic
)
239 ;;; arch-tag: 72d49161-25df-4072-9312-b182cdca7627
240 ;;; cal-coptic.el ends here