Integer types smaller than int are promoted when an operation is performed on them. If all values of the original type can be represented as an int, the value of the smaller type is converted to an int; otherwise, it is converted to an unsigned int (see INT02-C. Understand integer conversion rules). If the conversion is to a wider type, the original value is zero-extended for unsigned values or sign-extended for signed types. Arithmetic operations performed on ints yield the same values as on chars and shorts (at least in the low-order bits). HoweverConsequently, bitwise operations on integer types smaller than int may have unexpected results.
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In this example, a bitwise complement of port is first computed and then shifted 4 bits to the right. If both of these operations were are performed on an 8-bit unsigned integer, then result_8 would will have the value 0x0a. However, port will is first be promoted to a signed int, with the following results (on a typical architecture where type int is 32 bits wide):
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In this compliant solution, we truncate the negation back down the bitwise complement of port is converted back to 8 bits. Consequently, result_8 receives is assigned the expected value of 0x0aU.
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