IBM 1130 User Manual page 643

Section
Subsections Page
85
10
I
20
03
Searching the Index
Figure 85.1 illustrates a typical method of search-
ing an index.
Unlike pure sequential organization, which is
searched on the disk, indexed sequential gives an
index to search in core storage. The simplest
approach is to search the table sequentially, one
entry at a time, starting at the top. When you find
an equal-or-less-than condition, you have found
what you are looking for. The subroutine shown in
You would CALL the subroutine FINDM with the
known values of:
ITEM -- the item you are searching for
ITABL -- the name of the index table
LTABL -- the length of the index table
ISS -- the index table step size
NFILE -- the number of the file
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Figure 85. 1.
1/
FOR
*EXTENDED PRECISION
*TRANSFER TRACE
*ONE WORD INTEGERS
*LIST ALL
*ARITHMETIC TRACE
SU8ROUTIN~
FINDM(NREC,ITEM,NFILE,ITABL,LTABL,ISS,IER)
DIMENSION ITABL(l)
IER
=
1
DO 1 N
=
1 , LTABL
IF ( ITEM - ITABL(N) )
2 ,
2 ,
1
1
CONTINUE
C ITEM IS LARGER THAN THE LARG~ST VALUE IN THE INDEX TABLE
IER
=
2
RETURN
2 NREC
=
ISS
*
N
DO
3 N
=
1 ,
ISS
READ ( NFILE
t
NREC KEY
IF ( KEY - ITEM) 4 , 5 , 6
6 NREC
=
NREC -
1
3 CONTINUE
C ITEM IS NOT IN THE FILE IN THE AREA WHERE IT SHOULD BE
4
IER
=
3
5 RETURN
END
VARIABLE ALLOCATIONS
N (I ) =0000 KEY (I ) =0001
STATEMENT ALLOCATIONS
1 =0033
2
=0042 6
FEATURES SUPPORTED
TRANSFER TRACE
ARITHMETIC TRACE
ONE WORD INTEGERS
EXTENDED PRECISION
CALLED SUBPROGRAMS
=005B 3
SIAR SIIF SUBSC
SUBIN
SDRED
INTEGER CONSTANTS
1=0004 2=0005
3=0006
CORE REQUIREMENTS FOR FINDM
COMMON 0 VARIABLES
4 PROGRAM
END OF
CCMPI~ATION
=0001 4 =006A 5
SDI
108
=006E