r11722: add day-of-week

[kmrcl.git] / datetime.lisp

diff --git a/datetime.lisp b/datetime.lisp
index 59c1b3e140bdaf969cb36abcdf53313ffb56d214..8357da030b95b5e028d80711e072e6fb83cfdc30 100644 (file)
--- a/datetime.lisp
+++ b/datetime.lisp
@@ -32,9 +32,13 @@
                   "July" "August" "September" "October" "November"
                   "December")
                 (1- mn))
                   "July" "August" "September" "October" "November"
                   "December")
                 (1- mn))

-           (format nil "~A" dy) (format nil "~A" yr)
+           (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)
+    (pretty-date yr mn dy hr min sec)))

 
 (defun date-string (ut)
   (if (typep ut 'integer)
 
 (defun date-string (ut)
   (if (typep ut 'integer)


@@ -104,6 +108,20 @@
               mincol colinc minpad padchar
               (subseq monthstring 0 truncate)))))
 
               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
 ;;;; Daylight Saving Time calculations
 
 ;; Daylight Saving Time begins for most of the United States at 2