Mercury13

// write Intel word
void st::Stream::writeIW(uint16_t w)
{
    write(&w, sizeof(uint16_t));
}

// Возвращает остаток потока
// cu_minus = clipped unsigned minus
virtual Pos remainder() { return cu_minus<Pos>(size(),pos()); }

class IC {   // interface
public:
  virtual int getC() = 0;
  virtual ~IC() = default;
};

class C : public IC {
public:
  int getC() final { return 42; }
};

class B {
public:
  IC* buddy() const { return fBuddy; }
  void setBuddy(IC* aBuddy) { fBuddy = aBuddy; }
  void someJob() const { if (fBuddy) std::cout << fBuddy->getC() << std::endl; }
private:
  IC* fBuddy = nullptr;
};

class A {
public:
  A() { b.setBuddy(&c); }
private:
  C c;
  B b;
}

enum {
    DOUBLE_MANTISSA_BITS = 52,
    DOUBLE_MIN_EXPONENT = -1022,
    DOUBLE_EXPONENT_BIAS = 1023,
};

#define UC8x(X,Y,Z,T) (static_cast<uint64_t>(0x##X##Y##Z##T##ULL))
#define DOUBLE_MANTISSA_MASK     UC8x(000f, ffff, ffff, ffff)
#define DOUBLE_EXPONENT_MASK     UC8x(7ff0, 0000, 0000, 0000)
#define DOUBLE_EXPONENT_MASK_HI  UC4x(7ff0, 0000)
#define DOUBLE_IMPLICIT_BIT (DOUBLE_MANTISSA_MASK + 1)

    union DoubleInt {
        double asDouble;
        uint64_t asInt;
        struct {
            uint32_t lo, hi;
        } asIntel;
    ....
   }

    int DoubleInt::exponent() const
    {
        return static_cast<int>((
                      static_cast<int64_t>(asInt & DOUBLE_EXPONENT_MASK) >>
                      (DOUBLE_MANTISSA_BITS)) - DOUBLE_EXPONENT_BIAS);
    }

    uint64_t DoubleInt::unsafeMantissa() const
    {
        int ex = exponent();
        uint64_t bits = asInt & DOUBLE_MANTISSA_MASK;
        return (ex == DOUBLE_MIN_EXPONENT - 1)
          ? bits << 1
          : bits | DOUBLE_IMPLICIT_BIT;
    }

    bool DoubleInt::isPreciseInteger() const
    {
        // функцию isFinite() намеренно упустил, ибо она есть «в коробке» Delphi.
        // А вот в Си++ есть не во всех реализациях…
        return isFinite()
            && (asDouble == 0.0 ||
            DOUBLE_MANTISSA_BITS - numberOfTrailingZeros(unsafeMantissa()) <= exponent());
    }

int math::numberOfTrailingZeros(uint64_t i)
{
    uint32_t x, y;
    if (i == 0u) return 64;
    int n = 63;
    y = static_cast<uint32_t>(i);
    if (y != 0) { n = n -32; x = y; } else x = (int)(i >> 32);
    y = x << 16; if (y != 0) { n = n -16; x = y; }
    y = x << 8;  if (y != 0) { n = n - 8; x = y; }
    y = x << 4;  if (y != 0) { n = n - 4; x = y; }
    y = x << 2;  if (y != 0) { n = n - 2; x = y; }
    return n - ((x << 1) >> 31);
}

bool math::isPreciseInteger(double x)
{
    DoubleInt di;
    di.asDouble = x;
    return di.isPreciseInteger();
}