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IAR Embedded Workbench for RX 5.20

ATH-shift-bounds

In this section:
Synopsis

Out of range shifts were found.

Enabled by default

Yes

Severity/Certainty

Medium/Medium

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Full description

The right-hand operand of a shift operator might be negative or too large. A shift operator on an n-bit argument should only shift between 0 and n-1 bits. The behavior here is undefined; the code might work as intended, or data could become erroneous. This check is identical to MISRAC2004-12.8, MISRAC++2008-5-8-1, MISRAC2012-Rule-12.2.

Coding standards
CERT INT34-C

Do not shift a negative number of bits or more bits than exist in the operand

CWE 682

Incorrect Calculation

MISRA C:2004 12.8

(Required) 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.

MISRA C:2012 Rule-12.2

(Required) The right hand operand of a shift operator shall lie in the range zero to one less than the width in bits of the essential type of the left hand operand

MISRA C++ 2008 5-8-1

(Required) 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.

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;
}