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The right-shift operation may be implemented as either an arithmetic (signed) shift or a logical (unsigned) shift. If E1 in the expression E1 >> E2 has a signed type and a negative value, the resulting value is implementation-defined. Also, a bitwise shift can result in undefined behavior. (See INT34-C. Do not shift an expression by a negative number of bits or more bits than or by greater than or equal to the number of bits that exist in the operand.)
This noncompliant code example can result in an error condition on implementations in which an arithmetic shift is performed, and the sign bit is propagated as the number is shifted [Dowd 2006]:
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