pTAL Guidelines for TAL Programmers

Coding Guidelines

pTAL Guidelines for TAL Programmers—527256-002

2-42

Hardware Indicators: Test Only in an IF Statement

Guideline: Reference hardware indicators only in the conditional expression of an IF

statement.

In TAL, you can reference a hardware indicator in any expression. You must ensure

that the hardware indicator reflects the condition that you expect at the location in your

code where you reference it.

In pTAL, you can test a hardware indicator only in the conditional expression of an IF

statement. You cannot include a hardware indicator in any other type of expression.

Hardware Indicators: Test Only in Next Statement

Guideline: Test hardware indicators only in the statement that immediately follows the

statement that sets the indicator.

Example 2-45 on page 2-42, Example 2-46 on page 2-42, and Example 2-47 on

page 2-43 do not follow the guideline.

Example 2-45 on page 2-42 attempts to test the value of the condition code after

calling the READX system procedure. The move statement between the call to READX

and the IF statement, however, renders the test of the condition code invalid.

Because a move statement does not change the condition code, Example 2-45 on

page 2-42 works as a TNS process.

Example 2-46 on page 2-42 attempts to test for overflow following a signed arithmetic

operation. The USE statement, however, renders the test for $OVERFLOW invalid.

Example 2-47 on page 2-43 attempts to test the condition code following the signed

arithmetic operation in the conditional expression of the IF statement. Although the

BEGIN keyword is valid, the USE statement renders the test for CCG invalid.

Example 2-45. Invalid Condition Code Test After Procedure Call

CALL READX( fn, buffer, buffer_len, bytes_read);

save_buffer ':=' buffer FOR bytes_read BYTES;

IF < THEN... ! ERROR: Must test CCL immediately after CALL to

! READX procedure

Example 2-46. Invalid Overflow Test After Arithmetic Operation

i := i + 1;

USE j;

IF $OVERFLOW THEN... ! ERROR: $OVERFLOW must be tested

! immediately after assignment statement