Synopsis

Do not shift an expression by a negative number of bits or by greater than or equal to the number of bits that exist in the operand.

Enabled by default

Yes

Severity/Certainty

Low/Low

Full description

Bitwise shifts include left-shift operations of the form shift-expression << additive-expression and right-shift operations of the form shift-expression >> additive-expression. The standard integer promotions are first performed on the operands, each of which has an integer type. The type of the result is that of the promoted left operand. If the value of the right operand is negative or is greater than or equal to the width of the promoted left operand, the behavior is undefined. Do not shift an expression by a negative number of bits or by a number greater than or equal to the precision of the promoted left operand.

Coding standards

Code examples

The following code example fails the check and will give a warning:

unsigned int foo(unsigned int x, unsigned int y)
{ 
  int shift = 33; // too big
  return 3U << shift;
}

The following code example passes the check and will not give a warning about this issue:

unsigned int foo(unsigned int x)
{ 
  int y = 1;  // OK - this is within the correct range
  return x << y;
}