From ec23095166a703272c2f8fe21efaaef368399e98 Mon Sep 17 00:00:00 2001 From: "Edward M. Reingold" Date: Thu, 21 Sep 1995 02:54:58 +0000 Subject: [PATCH] Minor fixes; moved some code here from other calendar files. --- lisp/calendar/cal-dst.el | 56 ++++++++++++++++++++++++++++++++++++++-- 1 file changed, 54 insertions(+), 2 deletions(-) diff --git a/lisp/calendar/cal-dst.el b/lisp/calendar/cal-dst.el index f48a9feb1d9..598af905d99 100644 --- a/lisp/calendar/cal-dst.el +++ b/lisp/calendar/cal-dst.el @@ -1,6 +1,6 @@ ;;; cal-dst.el --- calendar functions for daylight savings rules. -;; Copyright (C) 1993, 1994 Free Software Foundation, Inc. +;; Copyright (C) 1993, 1994, 1995 Free Software Foundation, Inc. ;; Author: Paul Eggert ;; Edward M. Reingold @@ -250,7 +250,7 @@ it can't find." (list t1-name t0-name t2-rules t1-rules t2-time t1-time) ))))))))))) -;;; The following six defvars relating to daylight savings time should NOT be +;;; The following eight defvars relating to daylight savings time should NOT be ;;; marked to go into loaddefs.el where they would be evaluated when Emacs is ;;; dumped. These variables' appropriate values depend on the conditions under ;;; which the code is INVOKED; so it's inappropriate to initialize them when @@ -330,6 +330,58 @@ If the locale never uses daylight savings time, set this to nil.") calendar-daylight-savings-starts-time) "*Number of minutes after midnight that daylight savings time ends.") +(defun dst-in-effect (date) + "True if on absolute DATE daylight savings time is in effect. +Fractional part of DATE is time of day." + (let* ((year (extract-calendar-year + (calendar-gregorian-from-absolute (floor date)))) + (dst-starts (and (eval calendar-daylight-savings-starts) + (+ (calendar-absolute-from-gregorian + (eval calendar-daylight-savings-starts)) + (/ calendar-daylight-savings-starts-time + 60.0 24.0)))) + (dst-ends (and (eval calendar-daylight-savings-ends) + (+ (calendar-absolute-from-gregorian + (eval calendar-daylight-savings-ends)) + (/ (- calendar-daylight-savings-ends-time + calendar-daylight-time-offset) + 60.0 24.0))))) + (and (and dst-starts dst-ends + (or (and (< dst-starts dst-ends);; northern hemi. + (<= dst-starts date) (< date dst-ends)) + (and (< dst-ends dst-starts);; southern hemi. + (<= dst-starts date) (< date dst-ends)) + (and dst-starts (not dst-ends) (<= dst-starts date)) + (and dst-ends (not dst-starts) (< date dst-ends))))))) + +(defun dst-adjust-time (date time &optional style) + "Adjust, to account for dst on DATE, decimal fraction standard TIME. +Returns a list (date adj-time zone) where `date' and `adj-time' are the values +adjusted for `zone'; here `date' is a list (month day year), `adj-time' is a +decimal fraction time, and `zone' is a string. + +Optional parameter STYLE forces the result time to be standard time when its +value is 'standard and daylight savings time (if available) when its value is +'daylight. + +Conversion to daylight savings time is done according to +`calendar-daylight-savings-starts', `calendar-daylight-savings-ends', +`calendar-daylight-savings-starts-time', +`calendar-daylight-savings-ends-time', and +`calendar-daylight-savings-offset'." + + (let* ((rounded-abs-date (+ (calendar-absolute-from-gregorian date) + (/ (round (* 60 time)) 60.0 24.0))) + (dst (dst-in-effect rounded-abs-date)) + (time-zone (if dst + calendar-daylight-time-zone-name + calendar-standard-time-zone-name)) + (time (+ rounded-abs-date + (if dst (/ calendar-daylight-time-offset 24.0 60.0) 0)))) + (list (calendar-gregorian-from-absolute (truncate time)) + (* 24.0 (- time (truncate time))) + time-zone))) + (provide 'cal-dst) ;;; cal-dst.el ends here -- 2.39.2