;;; cal-persia.el --- calendar functions for the Persian calendar ;; Copyright (C) 1996, 1997 Free Software Foundation, Inc. ;; Author: Edward M. Reingold ;; Keywords: calendar ;; Human-Keywords: Persian calendar, calendar, diary ;; This file is part of GNU Emacs. ;; GNU Emacs is free software; you can redistribute it and/or modify ;; it under the terms of the GNU General Public License as published by ;; the Free Software Foundation; either version 2, or (at your option) ;; any later version. ;; GNU Emacs is distributed in the hope that it will be useful, ;; but WITHOUT ANY WARRANTY; without even the implied warranty of ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ;; GNU General Public License for more details. ;; You should have received a copy of the GNU General Public License ;; along with GNU Emacs; see the file COPYING. If not, write to the ;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, ;; Boston, MA 02110-1301, USA. ;;; Commentary: ;; This collection of functions implements the features of calendar.el and ;; diary.el that deal with the Persian calendar. ;; Technical details of all the calendrical calculations can be found in ;; ``Calendrical Calculations: The Millennium Edition'' by Edward M. Reingold ;; and Nachum Dershowitz, Cambridge University Press (2001). ;; Comments, corrections, and improvements should be sent to ;; Edward M. Reingold Department of Computer Science ;; (217) 333-6733 University of Illinois at Urbana-Champaign ;; reingold@cs.uiuc.edu 1304 West Springfield Avenue ;; Urbana, Illinois 61801 ;;; Code: (require 'cal-julian) (defvar persian-calendar-month-name-array ["Farvardin" "Ordibehest" "Xordad" "Tir" "Mordad" "Sahrivar" "Mehr" "Aban" "Azar" "Dey" "Bahman" "Esfand"]) (defvar persian-calendar-epoch (calendar-absolute-from-julian '(3 19 622)) "Absolute date of start of Persian calendar = March 19, 622 A.D. (Julian).") (defun persian-calendar-leap-year-p (year) "True if YEAR is a leap year on the Persian calendar." (< (mod (* (mod (mod (if (<= 0 year) ; No year zero (+ year 2346) (+ year 2347)) 2820) 768) 683) 2820) 683)) (defun persian-calendar-last-day-of-month (month year) "Return last day of MONTH, YEAR on the Persian calendar." (cond ((< month 7) 31) ((or (< month 12) (persian-calendar-leap-year-p year)) 30) (t 29))) (defun calendar-absolute-from-persian (date) "Compute absolute date from Persian date DATE. The absolute date is the number of days elapsed since the (imaginary) Gregorian date Sunday, December 31, 1 BC." (let ((month (extract-calendar-month date)) (day (extract-calendar-day date)) (year (extract-calendar-year date))) (if (< year 0) (+ (calendar-absolute-from-persian (list month day (1+ (mod year 2820)))) (* 1029983 (floor year 2820))) (+ (1- persian-calendar-epoch); Days before epoch (* 365 (1- year)) ; Days in prior years. (* 683 ; Leap days in prior 2820-year cycles (floor (+ year 2345) 2820)) (* 186 ; Leap days in prior 768 year cycles (floor (mod (+ year 2345) 2820) 768)) (floor; Leap years in current 768 or 516 year cycle (* 683 (mod (mod (+ year 2345) 2820) 768)) 2820) -568 ; Leap years in Persian years -2345...-1 (calendar-sum ; Days in prior months this year. m 1 (< m month) (persian-calendar-last-day-of-month m year)) day)))) ; Days so far this month. (defun calendar-persian-year-from-absolute (date) "Persian year corresponding to the absolute DATE." (let* ((d0 ; Prior days since start of 2820 cycles (- date (calendar-absolute-from-persian (list 1 1 -2345)))) (n2820 ; Completed 2820-year cycles (floor d0 1029983)) (d1 ; Prior days not in n2820 (mod d0 1029983)) (n768 ; 768-year cycles not in n2820 (floor d1 280506)) (d2 ; Prior days not in n2820 or n768 (mod d1 280506)) (n1 ; Years not in n2820 or n768 ; we want is ; (floor (+ (* 2820 d2) (* 2820 366)) 1029983)) ; but that causes overflow, so we use (let ((a (floor d2 366)); we use 366 as the divisor because ; (2820*366 mod 1029983) is small (b (mod d2 366))) (+ 1 a (floor (+ (* 2137 a) (* 2820 b) 2137) 1029983)))) (year (+ (* 2820 n2820); Complete 2820 year cycles (* 768 n768) ; Complete 768 year cycles (if ; Remaining years ; Last day of 2820 year cycle (= d1 1029617) (1- n1) n1) -2345))) ; Years before year 1 (if (< year 1) (1- year); No year zero year))) (defun calendar-persian-from-absolute (date) "Compute the Persian equivalent for absolute date DATE. The result is a list of the form (MONTH DAY YEAR). The absolute date is the number of days elapsed since the imaginary Gregorian date Sunday, December 31, 1 BC." (let* ((year (calendar-persian-year-from-absolute date)) (month ; Search forward from Farvardin (1+ (calendar-sum m 1 (> date (calendar-absolute-from-persian (list m (persian-calendar-last-day-of-month m year) year))) 1))) (day ; Calculate the day by subtraction (- date (1- (calendar-absolute-from-persian (list month 1 year)))))) (list month day year))) (defun calendar-persian-date-string (&optional date) "String of Persian date of Gregorian DATE. Defaults to today's date if DATE is not given." (let* ((persian-date (calendar-persian-from-absolute (calendar-absolute-from-gregorian (or date (calendar-current-date))))) (y (extract-calendar-year persian-date)) (m (extract-calendar-month persian-date))) (let ((monthname (aref persian-calendar-month-name-array (1- m))) (day (int-to-string (extract-calendar-day persian-date))) (dayname nil) (month (int-to-string m)) (year (int-to-string y))) (mapconcat 'eval calendar-date-display-form "")))) (defun calendar-print-persian-date () "Show the Persian calendar equivalent of the selected date." (interactive) (message "Persian date: %s" (calendar-persian-date-string (calendar-cursor-to-date t)))) (defun calendar-goto-persian-date (date &optional noecho) "Move cursor to Persian date DATE. Echo Persian date unless NOECHO is t." (interactive (persian-prompt-for-date)) (calendar-goto-date (calendar-gregorian-from-absolute (calendar-absolute-from-persian date))) (or noecho (calendar-print-persian-date))) (defun persian-prompt-for-date () "Ask for a Persian date." (let* ((today (calendar-current-date)) (year (calendar-read "Persian calendar year (not 0): " '(lambda (x) (/= x 0)) (int-to-string (extract-calendar-year (calendar-persian-from-absolute (calendar-absolute-from-gregorian today)))))) (completion-ignore-case t) (month (cdr (assoc (completing-read "Persian calendar month name: " (mapcar 'list (append persian-calendar-month-name-array nil)) nil t) (calendar-make-alist persian-calendar-month-name-array 1)))) (last (persian-calendar-last-day-of-month month year)) (day (calendar-read (format "Persian calendar day (1-%d): " last) '(lambda (x) (and (< 0 x) (<= x last)))))) (list (list month day year)))) (defun diary-persian-date () "Persian calendar equivalent of date diary entry." (format "Persian date: %s" (calendar-persian-date-string date))) (provide 'cal-persia) ;;; arch-tag: 2832383c-e4b4-4dc2-8ee9-cfbdd53e5e2d ;;; cal-persia.el ends here