false positive shiftTooManyBits (and other ternary based on caller conditiions)

[Daniel Black]

template <unsigned int width> class Bitmap
{
  static const int BITS_PER_ELEMENT= sizeof(unsigned long long) * 8;
  static const int ARRAY_ELEMENTS= (width + BITS_PER_ELEMENT - 1) / BITS_PER_ELEMENT;

  unsigned long long buffer[ARRAY_ELEMENTS];

private:
  unsigned long long bit_mask(unsigned int n) const
  {
    return ARRAY_ELEMENTS == 1 ? 1ULL << n : 1ULL << (n % BITS_PER_ELEMENT);
  }
public:
  void intersect_and_pad()
  {
    if (ARRAY_ELEMENTS > 1 && (width % BITS_PER_ELEMENT))
      buffer[ARRAY_ELEMENTS - 1]= bit_mask(width) - 1;
  }
};

static Bitmap<64> c;

/tmp/z.c++:11:39: error: Shifting 64-bit value by 64 bits is undefined behaviour [shiftTooManyBits]
    return ARRAY_ELEMENTS == 1 ? 1ULL << n : 1ULL << (n % BITS_PER_ELEMENT);
                                      ^
/tmp/z.c++:17:44: note: Calling function 'bit_mask', 1st argument '64' value is 64
      buffer[ARRAY_ELEMENTS - 1]= bit_mask(width) - 1;
                                           ^
/tmp/z.c++:11:39: note: Shift
    return ARRAY_ELEMENTS == 1 ? 1ULL << n : 1ULL << (n % BITS_PER_ELEMENT);

The condition in intersect_and_pad of ARRAY_ELEMENTS > 1 excludes the true element of the ternary and hence the error.

[CHR]

Thanks for reporting, ticket is here: https://trac.cppcheck.net/ticket/11496