P4040¶

Code: P4040
Message: Constant integer expression overflows its evaluation range

This error occurs when evaluating a constant integer expression at compile time produces a result that overflows the arithmetic range used for constant folding. Both operands are genuine compile-time constants – the expression is not rejected because it “isn’t constant” (see P4038), but because evaluating it is not possible.

The compiler folds constant integer arithmetic (+, -, *, /, MOD, **) at compile time so that later analysis and code generation see a plain literal rather than an expression tree. This folding is checked: if the result of an operation cannot be represented, the compiler reports P4040 instead of silently producing a wrapped or truncated value that would not match what the target hardware computes at runtime. Reporting the failure at compile time is preferable to letting an overflow surface later as a wrong runtime value with no obvious cause.

Example¶

The following code will generate error P4040:

PROGRAM main
VAR
    x : LINT := 100000000000000000000 * 100000000000000000000;
END_VAR
END_PROGRAM

To fix this error, use operand values that don’t overflow:

PROGRAM main
VAR
    x : LINT := 1000 * 1000;
END_VAR
END_PROGRAM

The same check applies to a constant expression anywhere in a program, not just a VAR initializer – for example, in an assignment statement:

PROGRAM main
VAR
    y : LINT;
END_VAR
y := 100000000000000000000 * 100000000000000000000;  (* Error *)
END_PROGRAM

If the values genuinely need to exceed what a single constant expression can represent, split the computation across multiple typed variables so each intermediate step stays within range, or compute the value at runtime instead of as a compile-time constant.

P4040¶

Example¶

See Also¶