TAL Reference Manual

Expressions

TAL Reference Manual—526371-001

4-16

Testing Hardware Indicators

Hardware indicators include condition code, carry, and overflow settings. Arithmetic

and conditional operations, assignments, and some file-system calls affect the setting

of the hardware indicators. To check the setting of a hardware indicator, use an IF

statement immediately after the operation that affects the hardware indicator.

Condition Code Indicator

The condition code indicator is set by a zero or a negative or positive result:

To check the state of the condition code indicator, use a relational operator (with no

operands) in a conditional expression. Using a relational operator with no operands is

equivalent to using the relational operator in a signed comparison against zero. When

used with no operands, signed and unsigned operators are equivalent. The result

returned by such a relational operator is as follows:

An example is:

IF < THEN ... ;

File-System Errors

File-system procedures signal their success or failure by returning an error number or

a condition code. Your program can preserve the returned condition code for later

operation as follows:

Result State of Condition Code Indicator

Negative CCL

0 CCE

Positive CCG

Relational Operator Result Returned

< or '<'

True if CCL

> or '>'

True if CCG

= or '='

True if CCE

<> or '<>'

True if not CCE

<= or '<='

True if CCL or CCE

>= or '>='

True if CCE or CCG