lisp/calendar/cal-persia.el

   1 ;;; cal-persia.el --- calendar functions for the Persian calendar
   2
   3 ;; Copyright (C) 1996-1997, 2001-2017 Free Software Foundation, Inc.
   4
   5 ;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
   6 ;; Maintainer: Glenn Morris <rgm@gnu.org>
   7 ;; Keywords: calendar
   8 ;; Human-Keywords: Persian calendar, calendar, diary
   9 ;; Package: calendar
  10
  11 ;; This file is part of GNU Emacs.
  12
  13 ;; GNU Emacs is free software: you can redistribute it and/or modify
  14 ;; it under the terms of the GNU General Public License as published by
  15 ;; the Free Software Foundation, either version 3 of the License, or
  16 ;; (at your option) any later version.
  17
  18 ;; GNU Emacs is distributed in the hope that it will be useful,
  19 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  20 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  21 ;; GNU General Public License for more details.
  22
  23 ;; You should have received a copy of the GNU General Public License
  24 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  25
  26 ;;; Commentary:
  27
  28 ;; See calendar.el.
  29
  30 ;;; Code:
  31
  32 (require 'calendar)
  33
  34 (defconst calendar-persian-month-name-array
  35   ["Farvardin" "Ordibehest" "Xordad" "Tir" "Mordad" "Sahrivar" "Mehr" "Aban"
  36    "Azar" "Dey" "Bahman" "Esfand"]
  37   "Names of the months in the Persian calendar.")
  38
  39 (eval-and-compile
  40   (autoload 'calendar-julian-to-absolute "cal-julian"))
  41
  42 (defconst calendar-persian-epoch
  43   (eval-when-compile (calendar-julian-to-absolute '(3 19 622)))
  44   "Absolute date of start of Persian calendar = March 19, 622 AD (Julian).")
  45
  46 (defun calendar-persian-leap-year-p (year)
  47   "True if YEAR is a leap year on the Persian calendar."
  48   (< (mod (* (mod (mod (if (<= 0 year)
  49                            (+ year 2346) ; no year zero
  50                          (+ year 2347))
  51                        2820)
  52                   768)
  53              683)
  54           2820)
  55      683))
  56
  57 (defun calendar-persian-last-day-of-month (month year)
  58   "Return last day of MONTH, YEAR on the Persian calendar."
  59   (cond
  60    ((< month 7) 31)
  61    ((or (< month 12) (calendar-persian-leap-year-p year)) 30)
  62    (t 29)))
  63
  64 (defun calendar-persian-to-absolute (date)
  65   "Compute absolute date from Persian date DATE.
  66 The absolute date is the number of days elapsed since the (imaginary)
  67 Gregorian date Sunday, December 31, 1 BC."
  68   (let ((month (calendar-extract-month date))
  69         (day (calendar-extract-day date))
  70         (year (calendar-extract-year date)))
  71     (if (< year 0)
  72         (+ (calendar-persian-to-absolute
  73             (list month day (1+ (mod year 2820))))
  74            (* 1029983 (floor year 2820)))
  75       (+ (1- calendar-persian-epoch)    ; days before epoch
  76          (* 365 (1- year))              ; days in prior years
  77          (* 683                  ; leap days in prior 2820-year cycles
  78             (floor (+ year 2345) 2820))
  79          (* 186                   ; leap days in prior 768 year cycles
  80             (floor (mod (+ year 2345) 2820) 768))
  81          (floor          ; leap years in current 768 or 516 year cycle
  82           (* 683 (mod (mod (+ year 2345) 2820) 768))
  83           2820)
  84          -568                 ; leap years in Persian years -2345...-1
  85          (calendar-sum        ; days in prior months this year
  86           m 1 (< m month)
  87           (calendar-persian-last-day-of-month m year))
  88          day))))                        ; days so far this month
  89
  90 (defun calendar-persian-year-from-absolute (date)
  91   "Persian year corresponding to the absolute DATE."
  92   (let* ((d0                   ; prior days since start of 2820 cycles
  93           (- date (calendar-persian-to-absolute (list 1 1 -2345))))
  94          (n2820                         ; completed 2820-year cycles
  95           (floor d0 1029983))
  96          (d1                            ; prior days not in n2820
  97           (mod d0 1029983))
  98          (n768                          ; 768-year cycles not in n2820
  99           (floor d1 280506))
 100          (d2                         ; prior days not in n2820 or n768
 101           (mod d1 280506))
 102          (n1        ; years not in n2820 or n768
 103           ;; Want:
 104           ;; (floor (+ (* 2820 d2) (* 2820 366)) 1029983))
 105           ;; but that causes overflow, so use the following.
 106           ;; Use 366 as the divisor because (2820*366 mod 1029983) is small.
 107           (let ((a (floor d2 366))
 108                 (b (mod d2 366)))
 109             (+ 1 a (floor (+ (* 2137 a) (* 2820 b) 2137) 1029983))))
 110          (year (+ (* 2820 n2820)        ; complete 2820 year cycles
 111                   (* 768 n768)          ; complete 768 year cycles
 112                   ;; Remaining years.
 113                   (if (= d1 1029617)    ; last day of 2820 year cycle
 114                       (1- n1)
 115                     n1)
 116                   -2345)))              ; years before year 1
 117     (if (< year 1)
 118         (1- year)                       ; no year zero
 119       year)))
 120
 121 (defun calendar-persian-from-absolute (date)
 122   "Compute the Persian equivalent for absolute date DATE.
 123 The result is a list of the form (MONTH DAY YEAR).
 124 The absolute date is the number of days elapsed since the imaginary
 125 Gregorian date Sunday, December 31, 1 BC."
 126   (let* ((year (calendar-persian-year-from-absolute date))
 127          (month                        ; search forward from Farvardin
 128           (1+ (calendar-sum m 1
 129                             (> date
 130                                (calendar-persian-to-absolute
 131                                 (list
 132                                  m
 133                                  (calendar-persian-last-day-of-month m year)
 134                                  year)))
 135                             1)))
 136          (day                       ; calculate the day by subtraction
 137           (- date (1- (calendar-persian-to-absolute
 138                        (list month 1 year))))))
 139     (list month day year)))
 140
 141 ;;;###cal-autoload
 142 (defun calendar-persian-date-string (&optional date)
 143   "String of Persian date of Gregorian DATE, default today."
 144   (let* ((persian-date (calendar-persian-from-absolute
 145                         (calendar-absolute-from-gregorian
 146                          (or date (calendar-current-date)))))
 147          (y (calendar-extract-year persian-date))
 148          (m (calendar-extract-month persian-date))
 149          (monthname (aref calendar-persian-month-name-array (1- m)))
 150          (day (number-to-string (calendar-extract-day persian-date)))
 151          (year (number-to-string y))
 152          (month (number-to-string m))
 153          dayname)
 154     (mapconcat 'eval calendar-date-display-form "")))
 155
 156 ;;;###cal-autoload
 157 (defun calendar-persian-print-date ()
 158   "Show the Persian calendar equivalent of the selected date."
 159   (interactive)
 160   (message "Persian date: %s"
 161            (calendar-persian-date-string (calendar-cursor-to-date t))))
 162
 163 (defun calendar-persian-read-date ()
 164   "Interactively read the arguments for a Persian date command.
 165 Reads a year, month, and day."
 166   (let* ((year (calendar-read
 167                 "Persian calendar year (not 0): "
 168                 (lambda (x) (not (zerop x)))
 169                 (number-to-string
 170                  (calendar-extract-year
 171                   (calendar-persian-from-absolute
 172                    (calendar-absolute-from-gregorian
 173                     (calendar-current-date)))))))
 174          (completion-ignore-case t)
 175          (month (cdr (assoc
 176                       (completing-read
 177                        "Persian calendar month name: "
 178                        (mapcar 'list
 179                                (append calendar-persian-month-name-array nil))
 180                        nil t)
 181                       (calendar-make-alist calendar-persian-month-name-array
 182                                            1))))
 183          (last (calendar-persian-last-day-of-month month year))
 184          (day (calendar-read
 185                (format "Persian calendar day (1-%d): " last)
 186                (lambda (x) (and (< 0 x) (<= x last))))))
 187     (list (list month day year))))
 188
 189 ;;;###cal-autoload
 190 (defun calendar-persian-goto-date (date &optional noecho)
 191   "Move cursor to Persian date DATE.
 192 Echo Persian date unless NOECHO is non-nil."
 193   (interactive (calendar-persian-read-date))
 194   (calendar-goto-date (calendar-gregorian-from-absolute
 195                        (calendar-persian-to-absolute date)))
 196   (or noecho (calendar-persian-print-date)))
 197
 198
 199 (defvar date)
 200
 201 ;; To be called from diary-list-sexp-entries, where DATE is bound.
 202 ;;;###diary-autoload
 203 (defun diary-persian-date ()
 204   "Persian calendar equivalent of date diary entry."
 205   (format "Persian date: %s" (calendar-persian-date-string date)))
 206
 207 (provide 'cal-persia)
 208
 209 ;;; cal-persia.el ends here