diff --git a/ChangeLog b/ChangeLog index a0186a4d2db909412a1429eefb51604e93d62201..2bd645b887939ef4df07d84594c1c3ece55def40 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,6 @@ +01 Jun 2007 Kevin Rosenberg <kevin@rosenberg.net> + * datetime.lisp: Add day-of-week + 07 Jan 2007 Kevin Rosenberg <kevin@rosenberg.net> * Version 1.94 * signals.lisp: Conditionalize Lispworks support to :unix *features* diff --git a/datetime.lisp b/datetime.lisp index 0346661cff309be2d75acf6480ccced646ab91bd..8357da030b95b5e028d80711e072e6fb83cfdc30 100644 --- a/datetime.lisp +++ b/datetime.lisp @@ -32,7 +32,7 @@ "July" "August" "September" "October" "November" "December") (1- mn)) - (format nil "~A" dy) + (format nil "~A" dy) (format nil "~A" yr) (format nil "~2,'0D:~2,'0D:~2,'0D" hr min 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