From e2fe2f5238d9619254fb3335156cef5b0704b1f5 Mon Sep 17 00:00:00 2001
From: Jim Blandy <jimb@redhat.com>
Date: Wed, 16 Jun 1993 23:12:21 +0000
Subject: [PATCH] *solar.el (solar-setup, solar-ephemeris-time,
 sunrise-sunset): Change         Universal Time (UT) to Coordinated Universal
 Time (UTC).         (solar-time-string): Use calendar-daylight-time-offset
 instead of         1 hr, and use calendar-daylight-savings-switchover-time
 instead of         midnight.  Add an optional parameter to allow forcing the
 use of         standard or daylight savings time.  Fix code so it works in   
      southern hemisphere (start of dst precedes end of dst in a        
 calendar year) and when dst either starts or ends in a calendar         year,
 but not both.

---
 lisp/calendar/solar.el | 58 +++++++++++++++++++++++++++++-------------
 1 file changed, 41 insertions(+), 17 deletions(-)

diff --git a/lisp/calendar/solar.el b/lisp/calendar/solar.el
index f9f582b9a46..24681df7b4f 100644
--- a/lisp/calendar/solar.el
+++ b/lisp/calendar/solar.el
@@ -72,7 +72,7 @@
   (if (not calendar-time-zone)
       (setq calendar-time-zone
             (solar-get-number
-             "Enter difference from Universal Time (in minutes): "))))
+             "Enter difference from Coordinated Universal Time (in minutes): "))))
 
 (defun solar-get-number (prompt)
   "Return a number from the minibuffer, prompting with PROMPT.
@@ -226,22 +226,46 @@ of hours.  Returns nil if the sun does not set at that location on that day."
 	(+ (- local-mean-sunset (solar-degrees-to-hours calendar-longitude))
 	   (/ calendar-time-zone 60.0))))))
 
-(defun solar-time-string (time date)
-  "Printable form for decimal fraction standard TIME on DATE.
+(defun solar-time-string (time date &optional style)
+  "Printable form for decimal fraction *standard* TIME on DATE.
+Optional parameter STYLE forces the time to be standard time when its value
+is 'standard and daylight savings time (if available) when its value is
+'daylight.
+
 Format used is given by `calendar-time-display-form'.  Converted to daylight
-savings time according to `calendar-daylight-savings-starts' and
-`calendar-daylight-savings-ends', if those variables are not nil."
+savings time according to `calendar-daylight-savings-starts',
+`calendar-daylight-savings-ends', `calendar-daylight-switchover-time', and
+`calendar-daylight-savings-offset'."
   (let* ((year (extract-calendar-year date))
-	 (abs-date (calendar-absolute-from-gregorian date))
-	 (dst (and calendar-daylight-savings-starts
-		   calendar-daylight-savings-ends
-		   (<= (calendar-absolute-from-gregorian
-			(eval calendar-daylight-savings-starts))
-		       abs-date)
-		   (< abs-date
-		      (calendar-absolute-from-gregorian
-		       (eval calendar-daylight-savings-ends)))))
-	 (time (if dst (1+ time) time))
+         (abs-date-and-time (+ (calendar-absolute-from-gregorian date)
+                               (/ time 24.0)))
+         (rounded-abs-date (+ abs-date-and-time (/ 1.0 60 24 2)));; half min
+         (dst-change-over
+          (/ (eval calendar-daylight-savings-switchover-time) 60.0 24.0))
+         (dst-starts (and calendar-daylight-savings-starts
+                          (+ (calendar-absolute-from-gregorian
+                              (eval calendar-daylight-savings-starts))
+                             dst-change-over)))
+         (dst-ends (and calendar-daylight-savings-ends
+                        (+ (calendar-absolute-from-gregorian
+                            (eval calendar-daylight-savings-ends))
+                           dst-change-over)))
+	 (dst (and (not (eq style 'standard))
+                   (or (eq style 'daylight)
+                       (and dst-starts dst-ends
+                            (or (and (< dst-starts dst-ends);; northern hemi.
+                                     (<= dst-starts rounded-abs-date)
+                                     (< rounded-abs-date dst-ends))
+                                (and (< dst-ends dst-starts);; southern hemi.
+                                     (or (< rounded-abs-date dst-ends)
+                                         (<= dst-starts rounded-abs-date)))))
+                       (and dst-starts (not dst-ends)
+                            (<= dst-starts rounded-abs-date))
+                       (and dst-ends (not dst-starts)
+                            (< rounded-abs-date dst-ends)))))
+         (time (if dst
+                   (+ time (/ (eval calendar-daylight-time-offset) 60.0))
+                 time))
 	 (time-zone (if dst
 			calendar-daylight-time-zone-name
 			calendar-standard-time-zone-name))
@@ -301,7 +325,7 @@ savings time according to `calendar-daylight-savings-starts' and
     app))
 
 (defun solar-ephemeris-correction (year)
-  "Difference in minutes between Ephemeris time an Universal time in YEAR.
+  "Difference in minutes between Ephemeris time and UTC in YEAR.
 Value is only an approximation."
   (let ((T (/ (- year 1900) 100.0)))
     (+ 0.41 (* 1.2053 T) (* 0.4992 T T))))
@@ -347,7 +371,7 @@ This function is suitable for execution in a .emacs file."
         (calendar-time-zone
          (if (< arg 16) calendar-time-zone
            (solar-get-number
-            "Enter difference from Universal Time (in minutes): ")))
+            "Enter difference from Coordinated Universal Time (in minutes): ")))
         (calendar-location-name
          (if (< arg 16) calendar-location-name
            (let ((float-output-format "%.1f"))
-- 
2.30.2