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From: natec@infohh.rmi.de (NATEC Institut GmbH)
Newsgroups: comp.lang.pascal
Subject: Day-of-week algorithm
Message-ID: <522@infohh.rmi.de>
Date: 12 Apr 89 06:31:00 GMT
Reply-To: natec@infohh.rmi.de (NATEC Institut GmbH)
Organization: RMI Net * Aachen/Hamburg/Flensburg * W.Germany
Lines: 40


try this approximation:

Function DayOfWeek ( Day, Month : Byte; Year : Word ) : Byte;
Function Leap : Byte; begin if Month>2 then Leap:=8 else Leap:=0 end;
begin
  DayOfWeek:= Trunc(Day+1+Int(Month/0.39)+(Year+Leap)/4+Int(Year*0.99)+
      Int(Year/400)) mod 7;
end;

- and, by the way, this is Easter:

Function Easter ( Year : Word ) : String;  { GAUSSIAN }
var d,e,f,M,N : Byte;
    a,s       : String;
begin
  if (Year<1700) or (Year>2199) then Easter:= 'don''t know' else begin
    Str (Year,a);
    M:= 24;
    if Year<1900 then M:= 23;
    N:= Trunc(Year/100) - 14;
    if N = 7 then N:= 6;
    d:= (19*(Year mod 19)+M) mod 30;
    e:= ( 2*(Year mod  4)+4*(Year mod 7)+6*d+N) mod 7;
    if 22+d+e < 32 then begin
      Str(22+d+e,s);
      Easter:= s+'.Mar.'+a
    end else begin
      f:= d+e-9;
      if  f = 26 then  f:= 19;
      if (f = 25) and (d = 28) and (Year mod 19 > 10) then f:= 18;
      Str (f,s);
      Easter:= s+'.Apr.'+a
    end
  end
end;

Dr Gerd C Schmerse  |  natec@infohh.rmi.de     |     ___    
NATEC Institut      |  49 40 88300170 (fax)    |    /o o\   
Hamburg, W.Germany  |  49 40 88300124 (voice)  | -m-"-U-"-m-