SA0020: Possibly assignment of truncated value to REAL variable

Detects operations on integer variables for which a truncated value could be assigned to a REAL data type variable

Justification: Static analysis issues an error when the result of an integer calculation is assigned to a REAL or LREAL variable. The programmer should be alerted to a possible incorrect interpretation of this kind of assignment: lrealvar := dintvar1 * dintvar2.

Because the value range of LREAL is greater than that of DINT, one could assume that the result of the calculation could always be represented in LREAL. But that is not the case. The processor calculates the result of the multiplication as an integer and then casts the result to LREAL. An overflow in the integer calculation would be lost. To work around the problem, the calculation has to be done as a REAL operation: lreal_var := TO_LREAL(dintvar1) * TO_LREAL(dintvar2).

Importance: High

PROGRAM PLC_PRG
VAR
    rX : LREAL;
    dI : DINT;
END_VAR

rX := dI * dI    // SA0020
rX := TO_LREAL(dI) * TO_LREAL(dI)    //no message