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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 / 2 E2. If E1 has a signed type and a negative value, the resulting value is implementation-defined and may be either an arithmetic (signed) shift as shown below or a logical (unsigned) shift.

This non-compliant code example fails to prevent to test if the right operand negative or is greater than or equal to the width of the promoted left operand, allowing undefined behavior.

int si1, si2, sresult;
unsigned int ui1, ui2, uresult;

sresult = si1 >> si2;
uresult = ui1 >> ui2;

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int si1, si2, sresult;
unsigned int ui1, ui2, result;

if ( (si1 < 0) || (si2 < 0) || (si2 >= sizeof(int)*CHAR_BIT) ) {
  /* handle error condition */
}
else {
  sresult = si1 >> si2;
}

if (ui2 >= sizeof(unsigned int)*CHAR_BIT) {
  /* handle error condition */
}
else {
  uresult = ui1 >> ui2;
}

As already noted, if the left operand has a signed type and a negative value, the resulting right shift could be either an arithmetic (signed) shift or a logical (unsigned) shift. For implementations in which an arithmetic shift is performed, and the sign bit can be propagated as the number is shifted.

int stringify;
char buf[sizeof("256")];   
sprintf(buf, "%u", stringify >> 24); 

If stringify has the value 0x80000000, stringify>> 24 evaluates to 0xFFFFFF80 and the subsequent call to sprintf() results in a buffer overflow.

For bit extraction, one remediation is to use the idiom ((number >> 24) & 0xff).

Exceptions

Unsigned integers can be allowed to exhibit modulo behavior if and only if

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\[[Dowd 06|AA. C References#Dowd 06]\] Chapter 6, "C Language Issues" 
\[[ISO/IEC 9899-1999|AA. C References#ISO/IEC 9899-1999]\] Section 6.5.7, "Bitwise shift operators"
\[[Seacord 05|AA. C References#Seacord 05]\] Chapter 5, "Integers"
\[[Viega 05|AA. C References#Viega 05]\] Section 5.2.7, "Integer overflow"
\[[ISO/IEC 03|AA. C References#ISO/IEC 03]\] Section 6.5.7, "Bitwise shift operators"