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93 lines
2.4 KiB
Plaintext
93 lines
2.4 KiB
Plaintext
/*
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* Author....: Paul Tucker
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* Email.....: <ptucker@sympatico.ca>
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*
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* While I can say that I wrote the program, the algorithm is from Donald
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* Knuth's The Art of Computer Programming, Section 1.3.2. So, the source
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* code is an original work by Paul Tucker and is placed in the public
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* domain
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*
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* Modification history:
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* ---------------------
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*
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* Rev 1.2 15 Aug 1991 23:05:28 GLENN
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* Forest Belt proofread/edited/cleaned up doc
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*
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* Rev 1.1 14 Jun 1991 19:51:42 GLENN
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* Minor edit to file header
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*
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* Rev 1.0 01 Apr 1991 01:01:16 GLENN
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* Nanforum Toolkit
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*
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*/
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FUNCTION ft_Easter( nYear )
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LOCAL nGold, nCent, nCorx, nCorz, nSunday, nEpact, nMoon
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LOCAL nMonth := 0, nDay := 0
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IF HB_ISSTRING( nYear )
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nYear := Val( nYear )
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ENDIF
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IF HB_ISDATE( nYear )
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nYear := Year( nYear )
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ENDIF
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IF HB_ISNUMERIC( nYear )
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IF nYear > 1582
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// <<nGold>> is Golden number of the year in the 19 year Metonic cycle
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nGold := nYear % 19 + 1
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// <<nCent>> is Century
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nCent := Int( nYear / 100 ) + 1
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// Corrections:
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// <<nCorx>> is the no. of years in which leap-year was dropped in order
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// to keep step with the sun
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nCorx := Int( ( 3 * nCent ) / 4 - 12 )
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// <<nCorz>> is a special correction to synchronize Easter with the moon's
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// orbit.
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nCorz := Int( ( 8 * nCent + 5 ) / 25 - 5 )
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// <<nSunday>> Find Sunday
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nSunday := Int( ( 5 * nYear ) / 4 - nCorx - 10 )
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// Set Epact <<nEpact>> (specifies occurance of a full moon)
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nEpact := Int( ( 11 * nGold + 20 + nCorz - nCorx ) % 30 )
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IF nEpact < 0
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nEpact += 30
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ENDIF
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IF ( nEpact == 25 .AND. nGold > 11 ) .OR. nEpact == 24
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++nEpact
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ENDIF
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// Find full moon - the <<nMoon>>th of MARCH is a "calendar" full moon
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nMoon := 44 - nEpact
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IF nMoon < 21
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nMoon += 30
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ENDIF
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// Advance to Sunday
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nMoon := Int ( nMoon + 7 - ( ( nSunday + nMoon ) % 7 ) )
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// Get Month and Day
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IF nMoon > 31
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nMonth := 4
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nDay := nMoon - 31
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ELSE
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nMonth := 3
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nDay := nMoon
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ENDIF
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ENDIF
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ELSE
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nYear := 0
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ENDIF
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RETURN hb_SToD( Str( nYear, 4 ) + PadL( nMonth, 2, "0" ) + PadL( Int( nDay ), 2, "0" ) )
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