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The C definition of the % operator implies the following behavior:

 1711 %  35  ->  21
 1711 % -35  ->  21
-1711 %  35  -> -21
-1711 % -35  -> -21

The result has the same sign as the dividend (the first operand in the expression).

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However, this noncompliant code example violates INT01-C. Use rsizesize_t or sizersize_t for all integer values representing the size of an object. There is also a possibility that (index + 1) could result in a signed integer overflow in violation of INT32-C. Ensure that operations on signed integers do not result in overflow.

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int insert(size_t* result, size_t index, int *list, size_t size, int value) {
  if (size != 0 && size != SIZE_MAX) {
    index = (index + 1) % size;
    list[index] = value;
    *result = index;
    return 1;
  }
  else {
    return 0;
  }
}

Risk Assessment

Incorrectly assuming that the result of the remainder operator for signed operands will always be positive can lead to an out-of-bounds memory accessor other flawed logic.

Automated Detection

Related Vulnerabilities

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

Related Guidelines

Bibliography

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