MISRA.BITS.NOT_UNSIGNED

Operand of bitwise operation is not unsigned integer.

MISRA-C Rule 12.7 (required): Bitwise operators shall not be applied to operands whose underlying type is signed.

[Implementation 17—19]

Bitwise operations (~, <<, <<=, >>, >>=, &, &=, ^, ^=, | and |=) are not normally meaningful on signed integers. Problems can arise if, for example, a right shift moves the sign bit into the number, or a left shift moves a numeric bit into the sign bit.

See section 6.10 for a description of underlying type.

MISRA-C++ Rule 5-0-21 (required): Bitwise operators shall only be applied to operands of unsigned underlying type.

[Implementation 5.8(3)]

Rationale

Bitwise operations (~, <<, <<=, >>, >>=, &, &=, ^, ^=, | and |=) are not normally meaningful on signed integers or enumeration constants. Additionally, an implementation-defined result is obtained if a right shift is applied to a negative value.

Example

if ( ( uint16_a & int16_b  ) == 0x1234U )     // Non-compliant
if ( ( uint16_a | uint16_b ) == 0x1234U )     // Compliant
if ( ~int16_a == 0x1234U )                    // Non-compliant
if ( ~uint16_a == 0x1234U )                   // Compliant