--- /dev/null
+;;; cal-persian.el --- calendar functions for the Persian calendar.
+
+;; Copyright (C) 1996 Free Software Foundation, Inc.
+
+;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
+;; 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, 675 Mass Ave, Cambridge, MA 02139, USA.
+
+;;; Commentary:
+
+;; This collection of functions implements the features of calendar.el and
+;; diary.el that deal with the Persian calendar.
+
+;; 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
+ (capitalize
+ (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 'capitalize))))
+ (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."
+ (calendar-persian-date-string (calendar-cursor-to-date t)))
+
+(provide 'cal-persian)
+
+;;; cal-persian.el ends here
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