Page History

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#include <limits.h>
#include <stddef.h>
#include <inttypes.h>
 
extern size_t popcount(uintmax_t);
#define PRECISION(x) popcount(x)
 
void func(signed long si_a, signed long si_b) {
  signed long result;
  if ((si_a < 0) || (si_b < 0) ||
      (si_b >= PRECISION(ULONG_MAX)) ||
      (si_a > (LONG_MAX >> si_b))) {
    /* Handle error */
  } else {
    result = si_a << si_b;
  }
  /* ... */
}

Noncompliant Code Example (Right Shift)

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Although shifting a negative number of bits or shifting a number of bits greater than or equal to the width of the promoted left operand is undefined behavior in C, the risk is generally low because processors frequently reduce the shift amount modulo the width of the type.

Automated Detection

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Related Guidelines

Key here (explains table format and definitions)

CERT-CWE Mapping Notes

Key here for mapping notes

CWE-758 and INT34-C

Independent( INT34-C, INT36-C, MEM30-C, MSC37-C, FLP32-C, EXP33-C, EXP30-C, ERR34-C, ARR32-C)

CWE-758 = Union( INT34-C, list) where list =

• Undefined behavior that results from anything other than incorrect bit shifting

CWE-682 and INT34-C

Independent( INT34-C, FLP32-C, INT33-C) CWE-682 = Union( INT34-C, list) where list =

• Incorrect calculations that do not involve out-of-range bit shifts

Bibliography

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