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a978be66 | 1 | ;;; cal-persia.el --- calendar functions for the Persian calendar. |
0e41f190 | 2 | |
a96a5fca | 3 | ;; Copyright (C) 1996, 1997 Free Software Foundation, Inc. |
0e41f190 ER |
4 | |
5 | ;; Author: Edward M. Reingold <reingold@cs.uiuc.edu> | |
6 | ;; Keywords: calendar | |
7 | ;; Human-Keywords: Persian calendar, calendar, 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 | |
6b091ffc ER |
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. | |
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25 | |
26 | ;;; Commentary: | |
27 | ||
28 | ;; This collection of functions implements the features of calendar.el and | |
29 | ;; diary.el that deal with the Persian calendar. | |
30 | ||
a96a5fca PE |
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). | |
34 | ||
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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 | |
40 | ||
41 | ;;; Code: | |
42 | ||
43 | (require 'cal-julian) | |
44 | ||
45 | (defvar persian-calendar-month-name-array | |
46 | ["Farvardin" "Ordibehest" "Xordad" "Tir" "Mordad" "Sahrivar" "Mehr" "Aban" | |
47 | "Azar" "Dey" "Bahman" "Esfand"]) | |
48 | ||
49 | (defvar persian-calendar-epoch (calendar-absolute-from-julian '(3 19 622)) | |
50 | "Absolute date of start of Persian calendar = March 19, 622 A.D. (Julian).") | |
51 | ||
52 | (defun persian-calendar-leap-year-p (year) | |
53 | "True if YEAR is a leap year on the Persian calendar." | |
54 | (< (mod (* (mod (mod (if (<= 0 year) | |
55 | ; No year zero | |
56 | (+ year 2346) | |
57 | (+ year 2347)) | |
58 | 2820) | |
59 | 768) | |
60 | 683) | |
61 | 2820) | |
62 | 683)) | |
63 | ||
64 | (defun persian-calendar-last-day-of-month (month year) | |
65 | "Return last day of MONTH, YEAR on the Persian calendar." | |
66 | (cond | |
67 | ((< month 7) 31) | |
68 | ((or (< month 12) (persian-calendar-leap-year-p year)) 30) | |
69 | (t 29))) | |
70 | ||
71 | (defun calendar-absolute-from-persian (date) | |
72 | "Compute absolute date from Persian date DATE. | |
73 | The absolute date is the number of days elapsed since the (imaginary) | |
74 | Gregorian date Sunday, December 31, 1 BC." | |
75 | (let ((month (extract-calendar-month date)) | |
76 | (day (extract-calendar-day date)) | |
77 | (year (extract-calendar-year date))) | |
78 | (if (< year 0) | |
79 | (+ (calendar-absolute-from-persian | |
80 | (list month day (1+ (mod year 2820)))) | |
81 | (* 1029983 (floor year 2820))) | |
82 | (+ (1- persian-calendar-epoch); Days before epoch | |
83 | (* 365 (1- year)) ; Days in prior years. | |
84 | (* 683 ; Leap days in prior 2820-year cycles | |
85 | (floor (+ year 2345) 2820)) | |
86 | (* 186 ; Leap days in prior 768 year cycles | |
87 | (floor (mod (+ year 2345) 2820) 768)) | |
88 | (floor; Leap years in current 768 or 516 year cycle | |
89 | (* 683 (mod (mod (+ year 2345) 2820) 768)) | |
90 | 2820) | |
91 | -568 ; Leap years in Persian years -2345...-1 | |
92 | (calendar-sum ; Days in prior months this year. | |
93 | m 1 (< m month) | |
94 | (persian-calendar-last-day-of-month m year)) | |
95 | day)))) ; Days so far this month. | |
96 | ||
97 | (defun calendar-persian-year-from-absolute (date) | |
98 | "Persian year corresponding to the absolute DATE." | |
99 | (let* ((d0 ; Prior days since start of 2820 cycles | |
100 | (- date (calendar-absolute-from-persian (list 1 1 -2345)))) | |
101 | (n2820 ; Completed 2820-year cycles | |
102 | (floor d0 1029983)) | |
103 | (d1 ; Prior days not in n2820 | |
104 | (mod d0 1029983)) | |
105 | (n768 ; 768-year cycles not in n2820 | |
106 | (floor d1 280506)) | |
107 | (d2 ; Prior days not in n2820 or n768 | |
108 | (mod d1 280506)) | |
109 | (n1 ; Years not in n2820 or n768 | |
110 | ; we want is | |
111 | ; (floor (+ (* 2820 d2) (* 2820 366)) 1029983)) | |
112 | ; but that causes overflow, so we use | |
113 | (let ((a (floor d2 366)); we use 366 as the divisor because | |
114 | ; (2820*366 mod 1029983) is small | |
115 | (b (mod d2 366))) | |
116 | (+ 1 a (floor (+ (* 2137 a) (* 2820 b) 2137) 1029983)))) | |
117 | (year (+ (* 2820 n2820); Complete 2820 year cycles | |
118 | (* 768 n768) ; Complete 768 year cycles | |
119 | (if ; Remaining years | |
120 | ; Last day of 2820 year cycle | |
121 | (= d1 1029617) | |
122 | (1- n1) | |
123 | n1) | |
124 | -2345))) ; Years before year 1 | |
125 | (if (< year 1) | |
126 | (1- year); No year zero | |
127 | year))) | |
128 | ||
129 | (defun calendar-persian-from-absolute (date) | |
130 | "Compute the Persian equivalent for absolute date DATE. | |
131 | The result is a list of the form (MONTH DAY YEAR). | |
132 | The absolute date is the number of days elapsed since the imaginary | |
133 | Gregorian date Sunday, December 31, 1 BC." | |
134 | (let* ((year (calendar-persian-year-from-absolute date)) | |
135 | (month ; Search forward from Farvardin | |
136 | (1+ (calendar-sum m 1 | |
137 | (> date | |
138 | (calendar-absolute-from-persian | |
139 | (list | |
140 | m | |
141 | (persian-calendar-last-day-of-month m year) | |
142 | year))) | |
143 | 1))) | |
144 | (day ; Calculate the day by subtraction | |
145 | (- date (1- (calendar-absolute-from-persian | |
146 | (list month 1 year)))))) | |
147 | (list month day year))) | |
148 | ||
149 | (defun calendar-persian-date-string (&optional date) | |
150 | "String of Persian date of Gregorian DATE. | |
151 | Defaults to today's date if DATE is not given." | |
152 | (let* ((persian-date (calendar-persian-from-absolute | |
153 | (calendar-absolute-from-gregorian | |
154 | (or date (calendar-current-date))))) | |
155 | (y (extract-calendar-year persian-date)) | |
156 | (m (extract-calendar-month persian-date))) | |
157 | (let ((monthname (aref persian-calendar-month-name-array (1- m))) | |
158 | (day (int-to-string (extract-calendar-day persian-date))) | |
159 | (dayname nil) | |
160 | (month (int-to-string m)) | |
161 | (year (int-to-string y))) | |
162 | (mapconcat 'eval calendar-date-display-form "")))) | |
163 | ||
164 | (defun calendar-print-persian-date () | |
165 | "Show the Persian calendar equivalent of the selected date." | |
166 | (interactive) | |
167 | (message "Persian date: %s" | |
168 | (calendar-persian-date-string (calendar-cursor-to-date t)))) | |
169 | ||
170 | (defun calendar-goto-persian-date (date &optional noecho) | |
171 | "Move cursor to Persian date DATE. | |
172 | Echo Persian date unless NOECHO is t." | |
173 | (interactive (persian-prompt-for-date)) | |
174 | (calendar-goto-date (calendar-gregorian-from-absolute | |
175 | (calendar-absolute-from-persian date))) | |
176 | (or noecho (calendar-print-persian-date))) | |
177 | ||
178 | (defun persian-prompt-for-date () | |
179 | "Ask for a Persian date." | |
180 | (let* ((today (calendar-current-date)) | |
181 | (year (calendar-read | |
182 | "Persian calendar year (not 0): " | |
183 | '(lambda (x) (/= x 0)) | |
184 | (int-to-string | |
185 | (extract-calendar-year | |
186 | (calendar-persian-from-absolute | |
187 | (calendar-absolute-from-gregorian today)))))) | |
188 | (completion-ignore-case t) | |
189 | (month (cdr (assoc | |
190 | (capitalize | |
191 | (completing-read | |
192 | "Persian calendar month name: " | |
193 | (mapcar 'list | |
194 | (append persian-calendar-month-name-array nil)) | |
195 | nil t)) | |
196 | (calendar-make-alist persian-calendar-month-name-array | |
197 | 1 'capitalize)))) | |
198 | (last (persian-calendar-last-day-of-month month year)) | |
199 | (day (calendar-read | |
200 | (format "Persian calendar day (1-%d): " last) | |
201 | '(lambda (x) (and (< 0 x) (<= x last)))))) | |
202 | (list (list month day year)))) | |
203 | ||
204 | (defun diary-persian-date () | |
205 | "Persian calendar equivalent of date diary entry." | |
edbf2694 | 206 | (format "Persian date: %s" (calendar-persian-date-string date))) |
0e41f190 | 207 | |
a978be66 | 208 | (provide 'cal-persia) |
0e41f190 | 209 | |
a978be66 | 210 | ;;; cal-persia.el ends here |