MISRA C++:2008 Rule 5-8-1

The right hand operand of a shift operator shall lie between zero and one less than the width in bits of the underlying type of the left hand operand

Description

The right hand operand of a shift operator shall lie between zero and one less than the width in bits of the underlying type of the left hand operand.¹

Rationale

When you use a shift operator, the value of the right-hand operand must be:

• Greater than or equal to zero.

• Less than the bit size of the data type of the left-hand operand.

If the above is not true, using a shift operator results in undefined behavior, which makes your program unpredictable and yields unexpected results.

Polyspace Implementation

Polyspace^® reports a rule violation when you use a negative operand on the right-hand side of a shift operator. Polyspace also reports a violation when the right-hand side of a shift operator is at least as large as the bit size of the data type of the left-hand operand.

Troubleshooting

If you expect a rule violation but Polyspace does not report it, see Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

Compliant and Noncompliant Use of Shift Operators

int shifted_output (int val) {
    if (val < 3) { 
        return val<<3; //Compliant
    }
    
    if (val > 3) { 
        return val>>-1; //Noncompliant
    } 
    
    return val<<33; //Noncompliant
}

In this example, the right-hand side of the shift operator in the first if statement is less than the size of int and greater than zero, so Polyspace does not report a violation. Because the right-hand operand of the shift operator is negative in the second if statement and greater than the size of int in the third, Polyspace reports a rule violation.

Check Information

Group: Expressions

Category: Required

Version History

Introduced in R2013b