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;;; time-date.el --- Date and time handling functions
;; Copyright (C) 1998,99 Free Software Foundation, Inc.
;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
;; Masanobu Umeda <umerin@mse.kyutech.ac.jp>
;; 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., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.
;;; Commentary:
;;; Code:
(require 'parse-time)
(defun date-to-time (date)
"Convert DATE into time."
(condition-case ()
(apply 'encode-time (parse-time-string date))
(error (error "Invalid date: %s" date))))
(defun time-to-seconds (time)
"Convert TIME to a floating point number."
(+ (* (car time) 65536.0)
(cadr time)
(/ (or (caddr time) 0) 1000000.0)))
(defun seconds-to-time (seconds)
"Convert SECONDS (a floating point number) to an Emacs time structure."
(list (floor seconds 65536)
(floor (mod seconds 65536))
(floor (* (- seconds (ffloor seconds)) 1000000))))
(defun time-less-p (t1 t2)
"Say whether time T1 is less than time T2."
(or (< (car t1) (car t2))
(and (= (car t1) (car t2))
(< (nth 1 t1) (nth 1 t2)))))
(defun days-to-time (days)
"Convert DAYS into time."
(let* ((seconds (* 1.0 days 60 60 24))
(rest (expt 2 16))
(ms (condition-case nil (floor (/ seconds rest))
(range-error (expt 2 16)))))
(list ms (condition-case nil (round (- seconds (* ms rest)))
(range-error (expt 2 16))))))
(defun time-since (time)
"Return the time since TIME, which is either an internal time or a date."
(when (stringp time)
;; Convert date strings to internal time.
(setq time (date-to-time time)))
(let* ((current (current-time))
(rest (when (< (nth 1 current) (nth 1 time))
(expt 2 16))))
(list (- (+ (car current) (if rest -1 0)) (car time))
(- (+ (or rest 0) (nth 1 current)) (nth 1 time)))))
(defun subtract-time (t1 t2)
"Subtract two internal times."
(let ((borrow (< (cadr t1) (cadr t2))))
(list (- (car t1) (car t2) (if borrow 1 0))
(- (+ (if borrow 65536 0) (cadr t1)) (cadr t2)))))
(defun date-to-day (date)
"Return the number of days between year 1 and DATE."
(time-to-days (date-to-time date)))
(defun days-between (date1 date2)
"Return the number of days between DATE1 and DATE2."
(- (date-to-day date1) (date-to-day date2)))
(defun date-leap-year-p (year)
"Return t if YEAR is a leap year."
(or (and (zerop (% year 4))
(not (zerop (% year 100))))
(zerop (% year 400))))
(defun time-to-day-in-year (time)
"Return the day number within the year of the date month/day/year."
(let* ((tim (decode-time time))
(month (nth 4 tim))
(day (nth 3 tim))
(year (nth 5 tim))
(day-of-year (+ day (* 31 (1- month)))))
(when (> month 2)
(setq day-of-year (- day-of-year (/ (+ 23 (* 4 month)) 10)))
(when (date-leap-year-p year)
(setq day-of-year (1+ day-of-year))))
day-of-year))
(defun time-to-days (time)
"The number of days between the Gregorian date 0001-12-31bce and TIME.
The Gregorian date Sunday, December 31, 1bce is imaginary."
(let* ((tim (decode-time time))
(month (nth 4 tim))
(day (nth 3 tim))
(year (nth 5 tim)))
(+ (time-to-day-in-year time) ; Days this year
(* 365 (1- year)) ; + Days in prior years
(/ (1- year) 4) ; + Julian leap years
(- (/ (1- year) 100)) ; - century years
(/ (1- year) 400)))) ; + Gregorian leap years
(defun safe-date-to-time (date)
"Parse DATE and return a time structure.
If DATE is malformed, a zero time will be returned."
(condition-case ()
(date-to-time date)
(error '(0 0))))
(provide 'time-date)
;;; time-date.el ends here
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