Right shift and signed integer

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From the following link:

INT34-C. Do not shift an expression by a negative number of bits or by greater than or equal to the number of bits that exist in the operand

Noncompliant Code Example (Right Shift)

The result of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has an unsigned type or if E1 has a signed type and a nonnegative value, the value of the result is the integral part of the quotient of E1 / 2E2. If E1 has a signed type and a negative value, the resulting value is implementation defined and can be either an arithmetic (signed) shift:

Arithmetic (signed) shift

Or a logical (unsigned) shift:

Logical (unsigned) shift

This noncompliant code example fails to test whether the right operand is greater than or equal to the width of the promoted left operand, allowing undefined behavior.

unsigned int ui1;
unsigned int ui2;
unsigned int uresult;
 
/* Initialize ui1 and ui2 */
 
uresult = ui1 >> ui2;

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 recommendation INT13-C. Use bitwise operators only on unsigned operands.

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