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;;;; Encode and decode universal times.
+;;; In August 2003, work was done in this file for more plausible
+;;; timezone handling after the unix timezone database runs out in
+;;; 2038. We assume that timezone rules are trending sane rather than
+;;; insane, so for all years after the end of time_t we apply the
+;;; rules for 2035/2036 instead of the actual date asked for. Making
+;;; the same assumption about the early 1900s would be less
+;;; reasonable, however, so please note that we're still broken for
+;;; local time between 1900-1-1 and 1901-12-13
+
+;;; It should be noted that 64 bit machines don't actually fix this
+;;; problem, at least as of 2003, because the Unix zonefiles are
+;;; specified in terms of 32 bit fields even on, say, the Alpha. So,
+;;; references to the range of time_t elsewhere in this file should
+;;; rightly be read as shorthand for the range of an signed 32 bit
+;;; number of seconds since 1970-01-01
+
+;;; I'm obliged to Erik Naggum's "Long, Painful History of Time" paper
+;;; <http://heim.ifi.uio.no/~enag/lugm-time.html> for the choice of epoch
+;;; here. By starting the year in March, we avoid having to test the month
+;;; whenever deciding whether to account for a leap day. 2000 is especially
+;;; special, because it's disvisible by 400, hence the start of a 400 year
+;;; leap year cycle
+
+;;; If a universal-time is after time_t runs out, we find its offset
+;;; from 1st March of whichever year it falls in, then add that to
+;;; 2035-3-1. This date has two relevant properties: (1) somewhere
+;;; near the end of time_t, and (2) preceding a leap year. Thus a
+;;; date which is e.g. 365.5 days from March 1st in its year will be
+;;; treated for timezone lookup as if it were Feb 29th 2036
+
+;;; This epoch is used only for fixing the timezones-outside-time_t
+;;; problem. Someday it would be nice to come back to this code and
+;;; see if the rest of the file and its references to Spice Lisp
+;;; history (Perq time base?) could be cleaned up any on this basis.
+;;; -- dan, 2003-08-08
+
+
;;; Subtract from the returned Internal-Time to get the universal
;;; time. The offset between our time base and the Perq one is 2145
;;; weeks and five days.
(daylight savings times) or NIL (standard time), and timezone."
(decode-universal-time (get-universal-time)))
+(defconstant +mar-1-2000+ #.(encode-universal-time 0 0 0 1 3 2000 0))
+(defconstant +mar-1-2035+ #.(encode-universal-time 0 0 0 1 3 2035 0))
+
+(defun years-since-mar-2000 (utime)
+ "Returns number of complete years since March 1st 2000, and remainder in seconds"
+ (let* ((days-in-year (* 86400 365))
+ (days-in-4year (+ (* 4 days-in-year) 86400))
+ (days-in-100year (- (* 25 days-in-4year) 86400))
+ (days-in-400year (+ (* 4 days-in-100year) 86400))
+ (offset (- utime +mar-1-2000+))
+ (year 0))
+ (labels ((whole-num (x y inc max)
+ (let ((w (truncate x y)))
+ (when (and max (> w max)) (setf w max))
+ (incf year (* w inc))
+ (* w y))))
+ (decf offset (whole-num offset days-in-400year 400 nil))
+ (decf offset (whole-num offset days-in-100year 100 3))
+ (decf offset (whole-num offset days-in-4year 4 25))
+ (decf offset (whole-num offset days-in-year 1 3))
+ (values year offset))))
+
+(defun truncate-to-unix-range (utime)
+ (let ((unix-time (- utime unix-to-universal-time)))
+ (if (< unix-time (ash 1 31))
+ unix-time
+ (multiple-value-bind (year offset) (years-since-mar-2000 utime)
+ (+ +mar-1-2035+ (- unix-to-universal-time) offset)))))
+
(defun decode-universal-time (universal-time &optional time-zone)
#!+sb-doc
"Converts a universal-time to decoded time format returning the following
(daylight NIL)
(timezone (cond
((null time-zone)
- (multiple-value-bind
- (ignore minwest dst)
- (sb!unix::get-timezone (- universal-time
- unix-to-universal-time))
+ (multiple-value-bind (ignore minwest dst)
+ (sb!unix::get-timezone
+ (truncate-to-unix-range universal-time))
(declare (ignore ignore))
(declare (fixnum minwest))
(setf daylight dst)
(incf sum days-in-month))
(coerce (nreverse reversed-result) 'simple-vector)))
+
(defun encode-universal-time (second minute hour date month year
&optional time-zone)
#!+sb-doc
(hours (+ hour (* days 24))))
(if time-zone
(+ second (* (+ minute (* (+ hours time-zone) 60)) 60))
- (let* ((minwest-guess
- (sb!unix::unix-get-minutes-west (- (* hours 60 60)
- unix-to-universal-time)))
- (guess (+ minute (* hours 60) minwest-guess))
- (minwest
- (sb!unix::unix-get-minutes-west (- (* guess 60)
- unix-to-universal-time))))
- (+ second (* (+ guess (- minwest minwest-guess)) 60))))))
+ ;; can't ask unix for times after 2037: this is only a problem
+ ;; if we need to query the system timezone
+ (if (> year 2037)
+ (labels ((leap-year-p (year)
+ (cond ((zerop (mod year 400)) t)
+ ((zerop (mod year 100)) t)
+ ((zerop (mod year 4)) t)
+ (t nil))))
+ (let* ((fake-year (if (leap-year-p year) 2036 2037))
+ (fake-time (encode-universal-time second minute hour
+ date month fake-year)))
+ (+ fake-time
+ (* 86400 (+ (* 365 (- year fake-year))
+ (- (leap-years-before year)
+ (leap-years-before fake-year)))))))
+ (let* ((minwest-guess
+ (sb!unix::unix-get-minutes-west
+ (- (* hours 60 60) unix-to-universal-time)))
+ (guess (+ minute (* hours 60) minwest-guess))
+ (minwest
+ (sb!unix::unix-get-minutes-west
+ (- (* guess 60) unix-to-universal-time))))
+ (+ second (* (+ guess (- minwest minwest-guess)) 60)))))))
\f
;;;; TIME
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