SA0066: Uses of temporary results

Detects the use of temporary results in statements with a data type which is less than the register size. In this case, the implicit cast may lead to undesirable results.

Justification: For performance reasons, CODESYS Static Analysis performs operations on the register width of the processor. Intermediate results are not truncated. This can lead to misinterpretations, as in the following case:

Example 78. Example

usintTest := 0; xError := usintTest - 1 <> 255;

In CODESYS, xError is TRUE in this case because the operation usintTest - 1 is typically executed as a 32-bit operation and the result is not cast to the byte size. Then the value 16#ffffffff (not equal to 255) is located in the register.

To avoid this, you need to cast the intermediate result explicitly:

xError := TO_USINT(usintTest - 1) <> 255;

Important

If this message is activated, then many less problematic locations in the code will be reported. Although a problem can only occur when the operation produces an overflow or underflow in the data type, the static analysis cannot differentiate between the individual locations.

If you include an explicit typecast in all reported locations, then the code will be much slower and less readable.

Importance: Low

Example 79. Example

PROGRAM PLC_PRG
VAR
    byTest:BYTE;
    liTest:LINT;
    xError:BOOL;
END_VAR

//type size smaller than register size;
byTest := 0;
IF (byTest - 1) <> 255 THEN //use of temporary result + implicit casting ->  SA0066
    xError := TRUE;
ELSE
    xError := FALSE;
END_IF

//type size equal to or bigger than register size;
liTest := 0;
IF (liTest - 1)  <> -1 THEN // use of temporary result and no implicit casting -> OK
    xError := TRUE;
ELSE
    xError := FALSE;
END_IF

Output in the Messages view:

SA0066: Uses of temporary results (byTest - USINT #1)