luhn algorithm in cobol

100001 IDENTIFICATION DIVISION.
100002 PROGRAM-ID.  LUHNTEST.
100003 ENVIRONMENT DIVISION.
100004 INPUT-OUTPUT SECTION.
100005 data division.
100006 WORKING-STORAGE SECTION.
100007 01  inp-card.
100008   03  inp-card-ch      pic x(01) occurs 20 times.
100009 01  ws-result          pic 9(01).
100010   88  pass-luhn-test             value 0.
100011
100012 PROCEDURE DIVISION.
100013     move "49927398716"       to inp-card
100014     perform test-card
100015     move "49927398717"       to inp-card
100016     perform test-card
100017     move "1234567812345678"  to inp-card
100018     perform test-card
100019     move "1234567812345670"  to inp-card
100020     perform test-card
100021     stop run
100022     .
100023 test-card.
100024     call "LUHN" using inp-card, ws-result
100025     if pass-luhn-test
100026       display "input=" inp-card "pass"
100027     else
100028       display "input=" inp-card "fail"
100029     .
100030
100031 END PROGRAM LUHNTEST.
100032 IDENTIFICATION DIVISION.
100033 PROGRAM-ID.  LUHN.
100034 ENVIRONMENT DIVISION.
100035 INPUT-OUTPUT SECTION.
100036 DATA DIVISION.
100037 WORKING-STORAGE SECTION.
100038 01  maxlen           pic 9(02) comp value 16.
100039 01  inplen           pic 9(02) comp value 0.
100040 01  i                pic 9(02) comp value 0.
100041 01  j                pic 9(02) comp value 0.
100042 01  l                pic 9(02) comp value 0.
100043 01  dw               pic 9(02) comp value 0.
100044 01  ws-total         pic 9(03) comp value 0.
100045 01  ws-prod          pic 99.
100046 01  filler redefines ws-prod.
100047   03  ws-prod-tens   pic 9.
100048   03  ws-prod-units  pic 9.
100049 01  ws-card.
100050   03  filler           occurs 16 times depending on maxlen.
100051     05  ws-card-ch     pic x(01).
100052     05  ws-card-digit redefines ws-card-ch  pic 9(01).
100053 LINKAGE SECTION.
100054 01  inp-card.
100055   03  inp-card-ch      pic x(01) occurs 20 times.
100056 01  ws-result          pic 9(01).
100057   88  pass-luhn-test             value 0.
100058
100059 PROCEDURE DIVISION using inp-card, ws-result.
100060     perform varying i from 1 by +1
100061     until i > maxlen
100062     or    inp-card-ch (i) = space
100063     end-perform
100064     compute l = i - 1
100065     compute inplen = l
100066     perform varying j from 1 by +1
100067     until j > inplen
100068       if l < 1
100069         move "0"             to ws-card-ch (j)
100070       else
100071         move inp-card-ch (l) to ws-card-ch (j)
100072         compute l = l - 1
100073       end-if
100074     end-perform
100075     move 0 to ws-total
100076     perform varying i from 1 by +1
100077     until i > inplen
100078       compute dw = 2 - (i - 2 * function integer (i / 2))
100079       compute ws-prod = ws-card-digit (i) * dw
100080       compute ws-total = ws-total
100081                        + ws-prod-tens
100082                        + ws-prod-units
100083     end-perform
100084     compute ws-result = ws-total - 10 * function integer (ws-total / 10)
100085     goback
100086     .
100087 END PROGRAM LUHN.