QA·C Help - 2861

	2861	Definite: Implementation-defined value resulting from left shift operation on expression of signed type.

Shift operations

A definite anomaly has been detected. The value of an expression of signed type is the subject of a left shift operation. Examination of the context indicates that the value being shifted will always be either negative or else of a positive value of magnitude such that the sign bit may be set. In either case the resulting value will be implementation-defined.

In general, shift operations on expressions of signed type should be avoided.

In the code below, the size of a long is assumed to be 32 bits. If the value of sl is greater than or equal to 0x10000000L, any operation which shifts left by more than 2 bits may generate a result which is negative.


/*PRQA S 294,1253,1277,1279,2017,2982,2983,2984,2986,3120,3198,3199,3203,3227,3408,4131 ++*/
void foo(long sl)
{
    long slr;

    if (sl > 0x0fffffffL)
    {
        slr = sl << 2;                /*      */
        slr = sl << 3;                /* 2861 */
        slr = sl << 4;                /* 2861 */
    }
}

See also:

2860 Constant: Implementation-defined value resulting from left shift operation on expression of signed type.
2862 Apparent: Implementation-defined value resulting from left shift operation on expression of signed type.
2863 Suspicious: Implementation-defined value resulting from left shift operation on expression of signed type.

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