RPGIII Get Day of Week Routine (Zeller Conguence)
Published by: **Bob Cozzi** on 22 Dec 2011 view comments(2)

This is the RPGIII source code to calculate the day of the week, using Zeller's Congruence formula:

***************************************************************** ** Zeller's Congruence in RPGIII by Bob Cozzi, July 2006 ** (c) 2006 by Bob Cozzi. All rights reserved. *********************************************************** ** Temp/work fields for calculation ITEMPS IDS I B 1 40DAYOWK I B 5 80TEMP1 I B 9 120TEMP2 ** ** Put the date into this Data Structure IZDATE IDS I 1 40NYEAR I 5 60NMONTH I 7 80NDAY ** Demo date is 23-July-1958 (should be a Wednesday) C Z-ADD1958 NYEAR C Z-ADD07 NMONTH C Z-ADD23 NDAY C EXSR ZDAY C MOVE *ON *INLR *********************************************************** ** This subroutine calculates the day of the week using ** Zeller's congruence. ** --Converted to RPGIII by Bob Cozzi, July 2006 ** (c) 2006 by Bob Cozzi. All rights reserved. ** Permission to use for any purpose is hereby granted ** provided credit to the copyright holder is included. ** ** Input fields: ** zDate Date in YYYYMMDD format ** nDay Day of month ** nYear Year ** nMonth Month *********************************************************** CSR ZDAY BEGSR ** If the month Jan or Feb, then adjust it to fit the algorythm. ** Also subtract 1 from the year in this situation. C NMONTH IFLT 3 C ADD 12 NMONTH C SUB 1 NYEAR C ENDIF ** ** Perform Zeller's formula to calculate the day of the week. C NMONTH MULT 13 TEMP1 C ADD 3 TEMP1 C DIV 5 TEMP1 C ADD NDAY TEMP1 C ADD NYEAR TEMP1 C NYEAR DIV 4 TEMP2 C ADD TEMP2 TEMP1 ** C NYEAR DIV 100 TEMP2 C SUB TEMP2 TEMP1 C NYEAR DIV 400 TEMP2 C ADD TEMP2 TEMP1 C DIV 7 TEMP1 C MVR DAYOWK ** ** At this point, we have the day of the week from Zeller. ** However, it is zero-based (Mon=0, Tues=1, Wed=3... etc.) ** This procedure is designed to return ones-based values ** as follows: (Sun=1, Mon=2, Tues=3... etc.) ** ** We need to convert the result from Zeller, as follows: ** If day is greater than 5, subtract 5 from the day. ** Otherwise, increase the day by 2. ** For example: Sun=6 so 6 - 5 = 1 ** Mon=0 so 0 + 2 = 2 ** Tue=1 so 1 + 2 = 3 ** Wed=2 so 2 + 2 = 4 ** Thu=3 so 3 + 2 = 5 ** Fri=4 so 4 + 2 = 6 ** Sat=5 so 5 + 2 = 7 ** ** If you prefer 0=Monday based return value, simply delete ** the code upto but NOT including the RETURN opcode. C DAYOWK IFGT 5 C SUB 5 DAYOWK C ELSE C ADD 2 DAYOWK C ENDIF CSR ENDZDY ENDSR

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Comment on: RPGIII Get Day of Week Routine (Zeller Conguence)

Posted: 5 years 6 months 7 days 6 hours 21 minutes ago

Posted: 5 years 6 months 7 days 6 hours 21 minutes ago

Wow, 2006 and still using RPGIII! Though I'm guessing from the last comment line that there was some thought given to making it an RPGIV procedure

Comment on: RPGIII Get Day of Week Routine (Zeller Conguence)

Posted: 5 years 6 months 7 days 5 hours 18 minutes ago

Edited: Thu, 22 Dec, 2011 at 15:49:56 (2014 days ago)

Posted: 5 years 6 months 7 days 5 hours 18 minutes ago

Edited: Thu, 22 Dec, 2011 at 15:49:56 (2014 days ago)

Haha, yes the shop I was consulting in needed RPGIII day of the week.

Originally we called an RPG IV program and did the CEExxxx thing. But then I found Zeller's formula and wanted to convert it to RPG. Since we don't really need it in RPG IV (at the time) I thought why not write it in RPGIII for the poor old bastards using III. Hence the subroutine.

Turns out to be one of my more widely-used routines (sadly). I'm archiving it here for future googler's or whatever displaces google, to find it.