10 Sep 2007 Kevin Rosenberg <kevin@rosenberg.net>

[kmrcl.git] / datetime.lisp

diff --git a/datetime.lisp b/datetime.lisp
index 0346661cff309be2d75acf6480ccced646ab91bd..b01bf33d323a8b0cb9c601a62a80609244f8a9de 100644 (file)
--- a/datetime.lisp
+++ b/datetime.lisp
@@ -26,15 +26,15 @@
     (decode-universal-time
      (encode-universal-time s m hour day month year))
     (values (elt '("Monday" "Tuesday" "Wednesday" "Thursday"
-                  "Friday" "Saturday" "Sunday")
-                wkday)
-           (elt '("January" "February" "March" "April" "May" "June"
-                  "July" "August" "September" "October" "November"
-                  "December")
-                (1- mn))
-           (format nil "~A" dy) 
+                   "Friday" "Saturday" "Sunday")
+                 wkday)
+            (elt '("January" "February" "March" "April" "May" "June"
+                   "July" "August" "September" "October" "November"
+                   "December")
+                 (1- mn))
+            (format nil "~A" dy)
             (format nil "~A" yr)
-           (format nil "~2,'0D:~2,'0D:~2,'0D" hr min sec))))
+            (format nil "~2,'0D:~2,'0D:~2,'0D" hr min sec))))
 
 (defun pretty-date-ut (&optional (tm (get-universal-time)))
   (multiple-value-bind (sec min hr dy mn yr) (decode-universal-time tm)
@@ -43,14 +43,14 @@
 (defun date-string (ut)
   (if (typep ut 'integer)
       (multiple-value-bind (sec min hr day mon year dow daylight-p zone)
-         (decode-universal-time ut)
-       (declare (ignore daylight-p zone))
-       (format nil "~[Mon~;Tue~;Wed~;Thu~;Fri~;Sat~;Sun~], ~d ~[Jan~;Feb~;Mar~;Apr~;May~;Jun~;Jul~;Aug~;Sep~;Oct~;Nov~;Dec~] ~d ~2,'0d:~2,'0d:~2,'0d"
-               dow
-               day
-               (1- mon)
-               year
-               hr min sec))))
+          (decode-universal-time ut)
+        (declare (ignore daylight-p zone))
+        (format nil "~[Mon~;Tue~;Wed~;Thu~;Fri~;Sat~;Sun~], ~d ~[Jan~;Feb~;Mar~;Apr~;May~;Jun~;Jul~;Aug~;Sep~;Oct~;Nov~;Dec~] ~d ~2,'0d:~2,'0d:~2,'0d"
+                dow
+                day
+                (1- mon)
+                year
+                hr min sec))))
 
 (defun print-seconds (secs)
   (print-float-units secs "sec"))
@@ -108,6 +108,20 @@
               mincol colinc minpad padchar
               (subseq monthstring 0 truncate)))))
 
+(defconstant* +zellers-adj+ #(0 3 2 5 0 3 5 1 4 6 2 4))
+
+(defun day-of-week (year month day)
+  "Day of week calculation using Zeller's Congruence.
+Input: The year y, month m (1 ≤ m ≤ 12) and day d (1 ≤ d ≤ 31).
+Output: n - the day of the week (Sunday = 0, Saturday = 6)."
+
+  (when (< month 3)
+    (decf year))
+  (mod
+   (+ year (floor year 4) (- (floor year 100)) (floor year 400)
+      (aref +zellers-adj+ (1- month)) day)
+   7))
+
 ;;;; Daylight Saving Time calculations
 
 ;; Daylight Saving Time begins for most of the United States at 2