SEI CERT C Coding Standard

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changes.mady.by.user Justin Pincar

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Comment: we are no longer concerned with wrapping for unsigned left shift

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This compliant solution eliminates the possibility of undefined behavior resulting from a left-shift operation on unsigned integers. Example solutions are provided for the fully compliant case (unsigned overflow is prohibited) and the exceptional case (modulo behavior is allowed).

Code Block
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unsigned int ui1;
unsigned int ui2;
unsigned int uresult;

unsigned int mod1; /* modulo behavior is allowed by INT34-EX1 */
unsigned int mod2; /* modulo behavior is allowed by INT34-EX1 */

/* Initialize ui1, ui2, mod1, and mod2ui2 */

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

if (mod2 >= sizeof(unsigned int)*CHAR_BIT) {
  /* handle error condition */
} else {
  /* modulo behavior is allowed by exception */
  uresult = mod1 << mod2;
}

Modulo behavior resulting from left shifting an unsigned integer type is permitted by this standard.

Noncompliant Code Example (Right Shift)

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