What Happens When You Right Shift an Unsigned Integer with a Shift Count Exceeding Its Width?

Right Shift Behavior with Exceeding Count

The question arises regarding the behavior of a right shift operation in C when the shift count exceeds the width of the data type. According to the C standard, right shifting an unsigned value with a non-negative count should result in the integral quotient of the original value divided by 2^E2. However, the user observed unexpected behavior with GCC on the Intel platform.

The issue stems from the fact that the C standard states the behavior is undefined if the right operand (shift count) is greater than or equal to the width of the promoted left operand (data value being shifted). In this case, since unsigned int is typically 32 bits or less, a shift count of 34 is considered undefined behavior.

GCC's warning "right shift count >= width of type" is indicative of this undefined behavior. The resulting value of 67108863 observed in the assembly code also corroborates this. Therefore, the issue lies not in GCC's implementation of the standard but rather in the undefined behavior caused by exceeding the data type's width in the shift operation.

The above is the detailed content of What Happens When You Right Shift an Unsigned Integer with a Shift Count Exceeding Its Width?. For more information, please follow other related articles on the PHP Chinese website!