43 lines
1.8 KiB
Text
43 lines
1.8 KiB
Text
begin % find the day of the week of dates using John Conway's Doomsday rule %
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% returns the day of the week (Sunday = 0, Monday = 1,...) for the date %
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% specified by ccyy, mm and dd %
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integer procedure dow ( integer value ccyy, mm, dd ) ;
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begin
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integer doomsday, anchorDay;
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logical isLeapYear;
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doomsday := ( % Tuesday % 2
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+ ( 5 * ( ccyy rem 4 ) )
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+ ( 4 * ( ccyy rem 100 ) )
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+ ( 6 * ( ccyy rem 400 ) )
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)
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rem 7;
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isLeapYear := ccyy rem 4 = 0 and ( ccyy rem 100 not = 0 or ccyy rem 400 = 0 );
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anchorDay := case mm of ( if isLeapYear then 4 else 3
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, if isLeapYear then 1 else 7
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, 7, 4, 2, 6, 4, 1, 5, 3, 7, 5
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);
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( doomsday + ( dd - anchorDay ) ) rem 7
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end dow ;
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begin % task test cases %
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% prints a test date and its day of the week %
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procedure testDow ( integer value ccyy, mm, dd ) ;
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write( i_w := 1, s_w := 0
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, ccyy
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, "-", mm div 10, mm rem 10
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, "-", dd div 10, dd rem 10
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, ": ", dayName( dow( ccyy, mm, dd ) )
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);
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string(9) array dayName ( 0 :: 6 );
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dayName( 0 ) := "Sunday"; dayName( 1 ) := "Monday"; dayName( 2 ) := "Tuesday";
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dayName( 3 ) := "Wednesday"; dayName( 4 ) := "Thursday"; dayName( 5 ) := "Friday";
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dayName( 6 ) := "Saturday";
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testDow( 1800, 1, 6 );
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testDow( 1875, 3, 29 );
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testDow( 1915, 12, 7 );
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testDow( 1970, 12, 23 );
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testDow( 2043, 5, 14 );
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testDow( 2077, 2, 12 );
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testDow( 2101, 4, 2 );
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testDow( 2022, 6, 19 )
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end
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end.
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