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In almost every case, an attempt to shift by a negative number of bits or by more bits than exist in the operand indicates a bug (logic error). This A logic error is different from overflow, where in which there is simply a representational deficiency. (See INT32-C. Ensure that operations on signed integers do not result in overflow.)

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The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with zeros. According to the C Standard, if E1 has an unsigned type, the value of the result is E1 * 2E2, reduced modulo one 1 more than the maximum value representable in the result type.

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Making assumptions about whether a right shift is implemented as an arithmetic (signed) shift or a logical (unsigned) shift can also lead to vulnerabilities. See INT13-C. Use bitwise operators only on unsigned operands.

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