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Operation
You can invoke
EXTSM, instead of the default run-time system SORT module, for quicker
execution of COBOL SORT and MERGE verbs in your program.
You invoke EXTSM in either of two ways:
* compile your program either with the CALLSORT"EXTSM"
directive specified on the command line or included in a $SET
statement of your program.
* call EXTSM explicitly using the CALL statement in your program.
See the section "CALL Interface" for further details.
When you perform a SORT operation on a data file, any duplicate keys
within the file are returned in random order. Setting the S run-time
switch forces all SORT statements within your file to be treated at
run-time as though you had specified the SORT...WITH DUPLICATES IN ORDER
statement. This means that duplicate keys are returned in the order they
were written.
Setting the S switch is the only available method of ensuring that
duplicate keys in a SORT statement are returned in order, as although you
can explicitly specify the WITH DUPLICATES IN ORDER phrase in your
program, it has no effect at run-time.
By default, this switch is set off (COBSW=-S). If no other switch is set
in COBSW, you can set it on as follows:
COBSW=+S
export COBSW
If COBSW already has other switches set, you need to add +S to it.
See Appendix E , Descriptions of Run-Time Switches for further
details.
CALL Interface
You can call EXTSM
explicitly to sort or merge your files, by including the following CALL
statement in your program:
call "EXTSM" using function-code, sort-fcd
where:
function-code is a two-byte code indicating the type of operation
to be performed. See the section Function Codes
later in this chapter for details of valid codes.
sort-fcd is the SORT file control descriptor (FCD). This is
an area in the Data Division that describes a file.
This contains pointers to the record area,
file-name, collating sequence, key definition block
(see the section "Key Definition Block" ) and
file definition block (see the section "File
Definition Block" ) of a file. See the section
"SORT File Control Descriptor" for further
information about the SORT FCD.
When using this command line, the normal COBOL syntax for SORT and MERGE
is not used. You, therefore, need to create a definition for each file
in the Data Division of your program which is involved in the SORT.
Function Codes.
Possible values for the function code parameter are:
x"FA01" Initiates the SORT operation. If the number of
USING files is other than zero, the sort starts
immediately, using the specified files as input.
If the number of GIVING files is other than zero,
the SORT operation returns from this call.
x"FA40" Initiates the MERGE operation. For this operation
the number of USING files MUST be other than zero.
It is assumed that each of these USING files
already has records sorted into order.
x"FAF3" Releases a record to the SORT operation. This
function is used only when the number of USING
files is zero.
x"FA10" Terminates the input stage of the SORT operation.
This function is used only when the number of USING
files is zero. It indicates that no more RELEASE
operations are performed. If the number of GIVING
files is other than zero, the SORT operation
terminates.
x"FAF5" Returns a record from the SORT or MERGE operation.
This function is used only when the number of
GIVING files is zero.
x"FA88" Terminates the SORT or MERGE operation, releasing
all memory allocated for the operation and deleting
any temporary files created. This function is used
only when the number of GIVING files is zero. It
indicates that no more RETURN operations are to be
performed.
SORT File Control Descriptor.
Set up the SORT file control descriptor (FCD) in the same way as the FCD
used by the Callable File Handler.
The SORT FCD used to interface to EXTSM has the following fields in
addition to, or overriding, the fields in the FCD described in Chapter 14
, Callable File Handler earlier in this manual:
---------------------------------------------------------------------
Offset Size Description of the field
---------------------------------------------------------------------
52 1 Number of USING files involved in the SORT
operation (this may be zero)
53 1 Number of GIVING files involved in the SORT
operation (this may be zero)
68 4 Pointer to the collating sequence (null if none
used)
72 4 Pointer to the File Definition Block where you
define the USING and GIVING files. See the section
File Definition Block for further information.
---------------------------------------------------------------------
Key Definition Block.
The Key Definition Block is used to describe the structure of the key to
be used in the SORT operation. There is a pointer to this block in the
SORT FCD at offset 64. See the section Key Definition Block in Chapter
14 , Callable File Handler earlier in this manual.
In the case of SORT operations, only one key is allowed, although this
key can have many components. Each of these components can be either
ascending or descending and can have one of many different numeric
formats. The first two bytes of the component definition are used as
follows:
Offset 0 - 1 byte:
bit 6 (value x"40") indicates DESCENDING key
bit 0 (value x"01") indicates that the data is in EBCDIC format
bit 1 (value x"02") indicates that SIGN is in EBCDIC format
Offset 1 - 1 byte:
bit 7 (value x"80") indicates that the field is NUMERIC
if bit 7 is set (numeric):
bit 6 (value x"40") indicates that the field is SIGNED NUMERIC
bit 5 (value x"20") indicates that the field is a non-display
field
If bit 5 is set (non-DISPLAY field):
bits 0 and 1 are used as follows:
0 indicates that the field is BINARY
1 indicates that the field is PACKED-DECIMAL
2 indicates that the field is COMP-X format
3 indicates that the field is COMP-5 format
bit 2 (value x"04") indicates floating point
If bit 5 is not set, (DISPLAY field)
but bit 6 is set (SIGNED field):
bits 0 and 1 are used as follows:
0 indicates SIGN TRAILING INCLUDED
1 indicates SIGN TRAILING SEPARATE
2 indicates SIGN LEADING INCLUDED
3 indicates SIGN LEADING SEPARATE
If bit 7 is not set (non-numeric):
Bit 1 is set if the collating sequence specified in the FCD is
to be applied to this field.
File Definition Block.
A File Definition Block is a table of pointers which point to the file
control descriptors for each of the USING and GIVING files involved in
the SORT operation. There is a pointer to this area in the SORT FCD at
offset 72. Its length is four times the total of the contents of the
fields at offsets 52 and 53.