If, for example, the left hand operand of a left-shift or right-shift is a 16-bit integer, then it is important to ensure that this is shifted only by a number in the range 0 to 15.

See Section 8.10 for a description of essential type and the limitations on the essential types for the operands of shift operators.

There are various ways of ensuring this rule is followed. The simplest is for the right hand operand to be a constant (whose value can then be statically checked). Use of an unsigned integer type will ensure that the operand is non-negative, so then only the upper limit needs to be checked (dynamically at run time or by review). Otherwise both limits will need to be checked.

Example

u8a = u8a << 7;                /* Compliant     */
u8a = u8a << 8;                /* Non-compliant */
u16a = ( uint16_t ) u8a << 9;  /* Compliant     */

To assist in understanding the following examples, it should be noted that the essential type of 1u is essentially unsigned char, whereas the essential type of 1UL is essentially unsigned long.

1u << 10u;                     /* Non-compliant */
( uint16_t ) 1u << 10u;        /* Compliant     */
1UL << 10u;                    /* Compliant     */