Document Number:     J4/02-0224

17 October 2002 

 

Page    1  of   3

Subject: 

Overlapping operands, replacing 02-0223

Author: 

Wim Ebbinkhuijsen

Date: 

2002-10-20

References:

1. 

 

 

 

COBOL 2002

2. 

 

 

 

COBOL 1985

DISCUSSION

I see an incompatibility with regard to the effect of overlapping operands for

statements in which the sending and the receiving operand are defined by the

same data description.

1. In COBOL 85 the paragraph on overlapping operands reads as follows:

"6.4.5 Overlapping Operands

When a sending and a receiving item in any statement share a part or all of

their storage areas, yet are not defined by the same data description entry, the

result of the execution of such a statement is undefined. In addition, the

results are undefined for some statements in which sending and receiving items

are defined by the same data description entry. These.cases are addressed in

the general rules associated with those statements."

2. In COBOL 2002 the paragraph on overlapping operands reads as follows:

"14.5.9 Overlapping operands

When a sending and a receiving data item in any statement share a part or all of their

storage areas, yet are not defined by the same data description entry, the result of the

execution of such a statement is undefined. For statements in which the sending and

receiving data items are defined by the same data description entry, the results of the

execution of the statement may be defined or undefined depending on the general

rules associated with the applicable statement. If there are no specific rules

addressing such overlapping operands, the results are undefined.

In the case of reference modification, the unique data item produced by reference

modification is not considered to be the same data description entry as any other data

description entry. Therefore, if an overlapping situation exists, the results of the

operation are undefined."

3. The definition of a sending and a receiving operand in COBOL 2002 is as follows:

"14.5.7 Sending and receiving operands

An operand is a sending operand if its contents prior to the execution of a statement

may be used by the execution

of the statement. An operand is a receiving operand if

its contents may be changed by the execution of the

statement. Operands may be

referenced either explicitly or implicitly by a statement. For some statements, an

Document Number:     J4/02-0224

17 October 2002 

 

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operand is both a sending operand and a receiving operand. The rules for a statement

specify whether operands

are sending operands, receiving operands, or both when

this is not clear from the context of the statement."

4. For items that are defined by the same data description there is a difference in the

two marked sentences (see items 1 and 2):

- COBOL 85 states impicitly that the results are defined

unless addressed otherwise in

the general rules for a specific statement.

- COBOL 2002 states explicitly that the results are undefined unless addressed

otherwise in the general rules for a specific statement.

4. I have checked all relevant statements to find the differences between COBOL 85

and COBOL 2002.

a. The arithmetic statements:

- The general rules for these statements in COBOL-85 refer to the paragraph on

overlapping operands (as quoted in item 1). Since there are are no specific rules on

overlapping operands specified for any of these statements, the results are defined.

- The general rules for these statements in COBOL-2002 refer to the paragraph on

overlapping operands (as quoted in item 2). Since there are are no specific rules on

overlapping operands specified for any of these statements, the results are undefined.

Therefore, the result of statements like

 

Add A to A

 

Subtract B from A giving A

 

Subtract function integer (A) from A

is defined in COBOL-85 but undefined in COBOL-2002.

It is even worse because normal statements like

 

Multiply B by A

 

Compute A = B / A

 

Add 1 to A

will also render undefined results since item A in these statements is both a sending

and a receiving operand.

b. The CALL statement:

- Neither the general rules for this statement in COBOL-85 nor in COBOL-2002 say

anything about overlapping operands. So, the results are defined in COBOL-85

(although I don't know what that means!) but undefined in COBOL-2002.

Document Number:     J4/02-0224

17 October 2002 

 

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Therefore, the result of

 

Call A using A returning A

is defined in COBOL-85 but undefined in COBOL-2002.

c. The MOVE statement:

- Neither the general rules for this statement in COBOL-85 nor in COBOL-2002 say

anything about overlapping operands. Therefore, the result of

 

Move A to A

is defined in COBOL-85 but undefined in COBOL-2002.

[For the INITIALIZE, STRING and  UNSTRING statements, both COBOL-85 and

COBOL-2002 state explicitly that the results are undefined.]

I surely hope that I see it all wrong …

Wim