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Minor fixes; moved some code here from other calendar files.

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Edward M. Reingold 1995-09-21 02:54:58 +00:00
parent 9fadf1a53e
commit ec23095166
1 changed files with 54 additions and 2 deletions
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56
lisp/calendar/cal-dst.el
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@ -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 <eggert@twinsun.com>
;; Edward M. Reingold <reingold@cs.uiuc.edu>
@ -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