r11722: add day-of-week

[kmrcl.git] / datetime.lisp

diff --git a/datetime.lisp b/datetime.lisp
index 52d45b2a43b044e6919f77778fd6f9d4f7218296..8357da030b95b5e028d80711e072e6fb83cfdc30 100644 (file)
--- a/datetime.lisp
+++ b/datetime.lisp
@@ -32,16 +32,20 @@
                   "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))))
 
+(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)
       (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" 
+       (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)
@@ -74,6 +78,9 @@
 (defun posix-time-to-utime (time)
   (+ time +posix-epoch+))
 
+(defun utime-to-posix-time (utime)
+  (- utime +posix-epoch+))
+
 ;; Monthnames taken from net-telent-date to support lml2
 
 (defvar *monthnames*
@@ -89,9 +96,10 @@
     (10 . "October")
     (11 . "November")
     (12 . "December")))
-    
+
 (defun monthname (stream arg colon-p at-p &optional width (mincol 0) (colinc 1) (minpad 0) (padchar #\Space))
   "Print the name of the month (1=January) corresponding to ARG on STREAM.  This is intended for embedding in a FORMAT directive: WIDTH governs the number of characters of text printed, MINCOL, COLINC, MINPAD, PADCHAR work as for ~A"
+  (declare (ignore colon-p))
   (let ((monthstring (cdr (assoc arg *monthnames*))))
     (if (not monthstring) (return-from monthname nil))
     (let ((truncate (if width (min width (length monthstring)) nil)))
@@ -100,7 +108,21 @@
               mincol colinc minpad padchar
               (subseq monthstring 0 truncate)))))
 
-;;;; Daylight Saving Time calculations 
+(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
 ;; a.m. on the first Sunday of April. Time reverts to standard time at