Sorting Strategies in COBOL
First, a follow-up note to our discussion of Python last month. It seems that BeOpen has gone out of business and the Pythonlabs people are now employed by Digital Creations, the authors of Zope, which is a Python Web development package. Now, on to this months business.
How many times have you just had some simple data in a table in your program that you wanted to sort? Seems like a waste of time to go through and write it to a file and sort the file and read it back in. The upcoming COBOL standard has a verb to allow you to sort tables (finally), but it will be some time before you get to use it.
Ive actually gotten a few e-mails recently asking me about this verb and sorting stategies, so I thought I would go over it. What I have this month is both a simple bubble sort and a more complex, but efficient, Shell sort. The bubble sort in Figure 1 only requires that we have two counters, one save buffer, and one table max variable, on top of the table data.
WORKING-STORAGE SECTION. 01 SAVE-CODE PIC X(04) VALUE SPACES. 01 S1 PIC S9(4) COMP VALUE 0. 01 S2 PIC S9(4) COMP VALUE 0. 01 TABLE-MAX PIC S9(4) COMP VALUE 0. 01 CODE-TABLE. 03 CODE-DATA PIC X(04) OCCURS 100 TIMES. PROCEDURE DIVISION. A1000-INIT. * * Do whatever steps are necessary to fill CODE-TABLE with the values * you are going to use in your program. Make sure to increment * TABLE-MAX for each entry you put in the table. * * Now we are going to perform a bubble sort of the table. * PERFORM VARYING S1 FROM 1 BY 1 UNTIL S1 = TABLE-MAX PERFORM VARYING S2 FROM S1 BY 1 UNTIL S2 > TABLE-MAX IF CODE-DATA(S2) < CODE-DATA(S1) MOVE CODE-DATA(S1) TO SAVE-CODE MOVE CODE-DATA(S2) TO CODE-DATA(S1) MOVE SAVE-CODE TO CODE-DATA(S2) END-IF END-PERFORM END-PERFORM.
As you can see, this is
pretty trivial, and is an easy to implement solution for simple
He says, When I
want to sort the array I use
* SHELL SORT ROUTINE * * This macro expects parameter 1 to be the element of the * table to be sorted. This sort compares the entire element. * Parameter 2 is the element hold area. Can be a higher * element of the table if you wish. * * To use this sort macro, you must COPY it into your program * in the 01 LEVEL area. Four (4) variables will be declared * and the $DEFINE for %SORTTABLE will be defined. * * Before invoking this macro you must set N-SUB to the * highest table element to be sorted. 01 I-SUB PIC S9(4) COMP. 01 J-SUB PIC S9(4) COMP. 01 M-SUB PIC S9(4) COMP. 01 N-SUB PIC S9(4) COMP. $DEFINE %SORTTABLE= IF N-SUB > 1 MOVE N-SUB TO M-SUB PERFORM TEST AFTER UNTIL M-SUB = 1 DIVIDE 2 INTO M-SUB ADD 1 TO M-SUB GIVING I-SUB PERFORM UNTIL I-SUB > N-SUB MOVE !1(I-SUB) TO !2 MOVE I-SUB TO J-SUB SUBTRACT M-SUB FROM J-SUB GIVING TALLY PERFORM UNTIL J-SUB <= M-SUB OR !1(TALLY) <= !2 MOVE !1(TALLY) TO !1(J-SUB) SUBTRACT M-SUB FROM J-SUB SUBTRACT M-SUB FROM J-SUB GIVING TALLY END-PERFORM MOVE !2 TO !1(J-SUB) ADD 1 TO I-SUB END-PERFORM END-PERFORM END-IF#
Shawn Gordon, whose S.M. Gordon & Associates firm supplies HP 3000 utilities, has worked with HP 3000s since 1983.
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