SA0052: Unusual shift operation

Detects shift operations (bit shift) on signed variables. In the case of shift operations on bitfield data types (‎Byte‎, ‎DWORD‎, ‎LWORD‎, ‎WORD‎), an error is not reported.

Justification: CODESYS permits shift operations on signed data types. However, these operations are unusual and can be confusing. The IEC 61131-3 standard does not provide for these kinds of operations. Therefore, they should be avoided in order to increase the portability of the code to other development systems.

Importance: Medium

Example

PROGRAM PLC_PRG
VAR
	iTemp : INT;
	dwTemp1 : DWORD;	
	byTemp2 : BYTE;
	diTemp3 : DINT;
	siTemp4 : SINT;
	liTemp5 : LINT;  
END_VAR

//the following lines each will cause an  SA0052:
iTemp := SHL(iTemp, BYTE#2);
diTemp3 := SHR(diTemp3, BYTE#4);
siTemp4 := ROL(siTemp4, BYTE#2);
liTemp5 := ROR(liTemp5, BYTE#2);

//no error SA0052 because DWORD and BYTE are bit field data types:
dwTemp1 := SHL(dwTemp1, BYTE#3);
byTemp2 := SHR(byTemp2, BYTE#1);

---> SA0052: Unusual shift operation