1;;; cal-julian.el --- calendar functions for the Julian calendar 2 3;; Copyright (C) 1995, 1997, 2001, 2002, 2003, 2004, 2005, 2006, 2007 4;; Free Software Foundation, Inc. 5 6;; Author: Edward M. Reingold <reingold@cs.uiuc.edu> 7;; Maintainer: Glenn Morris <rgm@gnu.org> 8;; Keywords: calendar 9;; Human-Keywords: Julian calendar, Julian day number, calendar, diary 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 2, or (at your option) 16;; 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; see the file COPYING. If not, write to the 25;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, 26;; Boston, MA 02110-1301, USA. 27 28;;; Commentary: 29 30;; This collection of functions implements the features of calendar.el and 31;; diary.el that deal with the Julian calendar. 32 33;; Technical details of all the calendrical calculations can be found in 34;; ``Calendrical Calculations: The Millennium Edition'' by Edward M. Reingold 35;; and Nachum Dershowitz, Cambridge University Press (2001). 36 37;;; Code: 38 39(defvar date) 40(defvar displayed-month) 41(defvar displayed-year) 42 43(require 'calendar) 44 45(defun calendar-julian-from-absolute (date) 46 "Compute the Julian (month day year) corresponding to the absolute DATE. 47The absolute date is the number of days elapsed since the (imaginary) 48Gregorian date Sunday, December 31, 1 BC." 49 (let* ((approx (/ (+ date 2) 366));; Approximation from below. 50 (year ;; Search forward from the approximation. 51 (+ approx 52 (calendar-sum y approx 53 (>= date (calendar-absolute-from-julian (list 1 1 (1+ y)))) 54 1))) 55 (month ;; Search forward from January. 56 (1+ (calendar-sum m 1 57 (> date 58 (calendar-absolute-from-julian 59 (list m 60 (if (and (= m 2) (= (% year 4) 0)) 61 29 62 (aref [31 28 31 30 31 30 31 31 30 31 30 31] 63 (1- m))) 64 year))) 65 1))) 66 (day ;; Calculate the day by subtraction. 67 (- date (1- (calendar-absolute-from-julian (list month 1 year)))))) 68 (list month day year))) 69 70(defun calendar-absolute-from-julian (date) 71 "The number of days elapsed between the Gregorian date 12/31/1 BC and DATE. 72The Gregorian date Sunday, December 31, 1 BC is imaginary." 73 (let ((month (extract-calendar-month date)) 74 (day (extract-calendar-day date)) 75 (year (extract-calendar-year date))) 76 (+ (calendar-day-number date) 77 (if (and (= (% year 100) 0) 78 (/= (% year 400) 0) 79 (> month 2)) 80 1 0);; Correct for Julian but not Gregorian leap year. 81 (* 365 (1- year)) 82 (/ (1- year) 4) 83 -2))) 84 85(defun calendar-julian-date-string (&optional date) 86 "String of Julian date of Gregorian DATE. 87Defaults to today's date if DATE is not given. 88Driven by the variable `calendar-date-display-form'." 89 (calendar-date-string 90 (calendar-julian-from-absolute 91 (calendar-absolute-from-gregorian 92 (or date (calendar-current-date)))) 93 nil t)) 94 95(defun calendar-print-julian-date () 96 "Show the Julian calendar equivalent of the date under the cursor." 97 (interactive) 98 (message "Julian date: %s" 99 (calendar-julian-date-string (calendar-cursor-to-date t)))) 100 101(defun calendar-goto-julian-date (date &optional noecho) 102 "Move cursor to Julian DATE; echo Julian date unless NOECHO is t." 103 (interactive 104 (let* ((today (calendar-current-date)) 105 (year (calendar-read 106 "Julian calendar year (>0): " 107 '(lambda (x) (> x 0)) 108 (int-to-string 109 (extract-calendar-year 110 (calendar-julian-from-absolute 111 (calendar-absolute-from-gregorian 112 today)))))) 113 (month-array calendar-month-name-array) 114 (completion-ignore-case t) 115 (month (cdr (assoc-string 116 (completing-read 117 "Julian calendar month name: " 118 (mapcar 'list (append month-array nil)) 119 nil t) 120 (calendar-make-alist month-array 1) t))) 121 (last 122 (if (and (zerop (% year 4)) (= month 2)) 123 29 124 (aref [31 28 31 30 31 30 31 31 30 31 30 31] (1- month)))) 125 (day (calendar-read 126 (format "Julian calendar day (%d-%d): " 127 (if (and (= year 1) (= month 1)) 3 1) last) 128 '(lambda (x) 129 (and (< (if (and (= year 1) (= month 1)) 2 0) x) 130 (<= x last)))))) 131 (list (list month day year)))) 132 (calendar-goto-date (calendar-gregorian-from-absolute 133 (calendar-absolute-from-julian date))) 134 (or noecho (calendar-print-julian-date))) 135 136(defun holiday-julian (month day string) 137 "Holiday on MONTH, DAY (Julian) called STRING. 138If MONTH, DAY (Julian) is visible, the value returned is corresponding 139Gregorian date in the form of the list (((month day year) STRING)). Returns 140nil if it is not visible in the current calendar window." 141 (let ((m1 displayed-month) 142 (y1 displayed-year) 143 (m2 displayed-month) 144 (y2 displayed-year) 145 (year)) 146 (increment-calendar-month m1 y1 -1) 147 (increment-calendar-month m2 y2 1) 148 (let* ((start-date (calendar-absolute-from-gregorian 149 (list m1 1 y1))) 150 (end-date (calendar-absolute-from-gregorian 151 (list m2 (calendar-last-day-of-month m2 y2) y2))) 152 (julian-start (calendar-julian-from-absolute start-date)) 153 (julian-end (calendar-julian-from-absolute end-date)) 154 (julian-y1 (extract-calendar-year julian-start)) 155 (julian-y2 (extract-calendar-year julian-end))) 156 (setq year (if (< 10 month) julian-y1 julian-y2)) 157 (let ((date (calendar-gregorian-from-absolute 158 (calendar-absolute-from-julian 159 (list month day year))))) 160 (if (calendar-date-is-visible-p date) 161 (list (list date string))))))) 162 163(defun diary-julian-date () 164 "Julian calendar equivalent of date diary entry." 165 (format "Julian date: %s" (calendar-julian-date-string date))) 166 167(defun calendar-absolute-from-astro (d) 168 "Absolute date of astronomical (Julian) day number D." 169 (- d 1721424.5)) 170 171(defun calendar-astro-from-absolute (d) 172 "Astronomical (Julian) day number of absolute date D." 173 (+ d 1721424.5)) 174 175(defun calendar-astro-date-string (&optional date) 176 "String of astronomical (Julian) day number after noon UTC of Gregorian DATE. 177Defaults to today's date if DATE is not given." 178 (int-to-string 179 (ceiling 180 (calendar-astro-from-absolute 181 (calendar-absolute-from-gregorian 182 (or date (calendar-current-date))))))) 183 184(defun calendar-print-astro-day-number () 185 "Show astronomical (Julian) day number after noon UTC on date shown by cursor." 186 (interactive) 187 (message 188 "Astronomical (Julian) day number (at noon UTC): %s.0" 189 (calendar-astro-date-string (calendar-cursor-to-date t)))) 190 191(defun calendar-goto-astro-day-number (daynumber &optional noecho) 192 "Move cursor to astronomical (Julian) DAYNUMBER. 193Echo astronomical (Julian) day number unless NOECHO is t." 194 (interactive (list (calendar-read 195 "Astronomical (Julian) day number (>1721425): " 196 '(lambda (x) (> x 1721425))))) 197 (calendar-goto-date 198 (calendar-gregorian-from-absolute 199 (floor 200 (calendar-absolute-from-astro daynumber)))) 201 (or noecho (calendar-print-astro-day-number))) 202 203(defun diary-astro-day-number () 204 "Astronomical (Julian) day number diary entry." 205 (format "Astronomical (Julian) day number at noon UTC: %s.0" 206 (calendar-astro-date-string date))) 207 208(provide 'cal-julian) 209 210;;; arch-tag: 0520acdd-1c60-4188-9aa8-9b8c24d856ae 211;;; cal-julian.el ends here 212