1 ;;; cal-persia.el --- calendar functions for the Persian calendar
3 ;; Copyright (C) 1996, 1997 Free Software Foundation, Inc.
5 ;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
7 ;; Human-Keywords: Persian 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 Persian calendar.
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 persian-calendar-month-name-array
48 ["Farvardin" "Ordibehest" "Xordad" "Tir" "Mordad" "Sahrivar" "Mehr" "Aban"
49 "Azar" "Dey" "Bahman" "Esfand"])
51 (defvar persian-calendar-epoch (calendar-absolute-from-julian '(3 19 622))
52 "Absolute date of start of Persian calendar = March 19, 622 A.D. (Julian).")
54 (defun persian-calendar-leap-year-p (year)
55 "True if YEAR is a leap year on the Persian calendar."
56 (< (mod (* (mod (mod (if (<= 0 year)
66 (defun persian-calendar-last-day-of-month (month year)
67 "Return last day of MONTH, YEAR on the Persian calendar."
70 ((or (< month 12) (persian-calendar-leap-year-p year)) 30)
73 (defun calendar-absolute-from-persian (date)
74 "Compute absolute date from Persian date DATE.
75 The absolute date is the number of days elapsed since the (imaginary)
76 Gregorian date Sunday, December 31, 1 BC."
77 (let ((month (extract-calendar-month date))
78 (day (extract-calendar-day date))
79 (year (extract-calendar-year date)))
81 (+ (calendar-absolute-from-persian
82 (list month day (1+ (mod year 2820))))
83 (* 1029983 (floor year 2820)))
84 (+ (1- persian-calendar-epoch); Days before epoch
85 (* 365 (1- year)) ; Days in prior years.
86 (* 683 ; Leap days in prior 2820-year cycles
87 (floor (+ year 2345) 2820))
88 (* 186 ; Leap days in prior 768 year cycles
89 (floor (mod (+ year 2345) 2820) 768))
90 (floor; Leap years in current 768 or 516 year cycle
91 (* 683 (mod (mod (+ year 2345) 2820) 768))
93 -568 ; Leap years in Persian years -2345...-1
94 (calendar-sum ; Days in prior months this year.
96 (persian-calendar-last-day-of-month m year))
97 day)))) ; Days so far this month.
99 (defun calendar-persian-year-from-absolute (date)
100 "Persian year corresponding to the absolute DATE."
101 (let* ((d0 ; Prior days since start of 2820 cycles
102 (- date (calendar-absolute-from-persian (list 1 1 -2345))))
103 (n2820 ; Completed 2820-year cycles
105 (d1 ; Prior days not in n2820
107 (n768 ; 768-year cycles not in n2820
109 (d2 ; Prior days not in n2820 or n768
111 (n1 ; Years not in n2820 or n768
113 ; (floor (+ (* 2820 d2) (* 2820 366)) 1029983))
114 ; but that causes overflow, so we use
115 (let ((a (floor d2 366)); we use 366 as the divisor because
116 ; (2820*366 mod 1029983) is small
118 (+ 1 a (floor (+ (* 2137 a) (* 2820 b) 2137) 1029983))))
119 (year (+ (* 2820 n2820); Complete 2820 year cycles
120 (* 768 n768) ; Complete 768 year cycles
121 (if ; Remaining years
122 ; Last day of 2820 year cycle
126 -2345))) ; Years before year 1
128 (1- year); No year zero
131 (defun calendar-persian-from-absolute (date)
132 "Compute the Persian equivalent for absolute date DATE.
133 The result is a list of the form (MONTH DAY YEAR).
134 The absolute date is the number of days elapsed since the imaginary
135 Gregorian date Sunday, December 31, 1 BC."
136 (let* ((year (calendar-persian-year-from-absolute date))
137 (month ; Search forward from Farvardin
138 (1+ (calendar-sum m 1
140 (calendar-absolute-from-persian
143 (persian-calendar-last-day-of-month m year)
146 (day ; Calculate the day by subtraction
147 (- date (1- (calendar-absolute-from-persian
148 (list month 1 year))))))
149 (list month day year)))
151 (defun calendar-persian-date-string (&optional date)
152 "String of Persian date of Gregorian DATE.
153 Defaults to today's date if DATE is not given."
154 (let* ((persian-date (calendar-persian-from-absolute
155 (calendar-absolute-from-gregorian
156 (or date (calendar-current-date)))))
157 (y (extract-calendar-year persian-date))
158 (m (extract-calendar-month persian-date)))
159 (let ((monthname (aref persian-calendar-month-name-array (1- m)))
160 (day (int-to-string (extract-calendar-day persian-date)))
162 (month (int-to-string m))
163 (year (int-to-string y)))
164 (mapconcat 'eval calendar-date-display-form ""))))
166 (defun calendar-print-persian-date ()
167 "Show the Persian calendar equivalent of the selected date."
169 (message "Persian date: %s"
170 (calendar-persian-date-string (calendar-cursor-to-date t))))
172 (defun calendar-goto-persian-date (date &optional noecho)
173 "Move cursor to Persian date DATE.
174 Echo Persian date unless NOECHO is t."
175 (interactive (persian-prompt-for-date))
176 (calendar-goto-date (calendar-gregorian-from-absolute
177 (calendar-absolute-from-persian date)))
178 (or noecho (calendar-print-persian-date)))
180 (defun persian-prompt-for-date ()
181 "Ask for a Persian date."
182 (let* ((today (calendar-current-date))
184 "Persian calendar year (not 0): "
185 '(lambda (x) (/= x 0))
187 (extract-calendar-year
188 (calendar-persian-from-absolute
189 (calendar-absolute-from-gregorian today))))))
190 (completion-ignore-case t)
193 "Persian calendar month name: "
195 (append persian-calendar-month-name-array nil))
197 (calendar-make-alist persian-calendar-month-name-array
199 (last (persian-calendar-last-day-of-month month year))
201 (format "Persian calendar day (1-%d): " last)
202 '(lambda (x) (and (< 0 x) (<= x last))))))
203 (list (list month day year))))
205 (defun diary-persian-date ()
206 "Persian calendar equivalent of date diary entry."
207 (format "Persian date: %s" (calendar-persian-date-string date)))
209 (provide 'cal-persia)
211 ;;; arch-tag: 2832383c-e4b4-4dc2-8ee9-cfbdd53e5e2d
212 ;;; cal-persia.el ends here