FixedPoint<Typ,FracBits> fast_sqrt() const
	{
		if (Data <= 0) return 0;
		int ld = (31-__builtin_clz(Data)) - FracBits;
		if (ld >= 0)
		{
			if (ld >= ((31-FracBits)/2)-1)
			{
				unsigned long long sq = (((unsigned long long)Data)*Data);
				unsigned int a = (6ULL << (ld+FracBits)) ;
				unsigned long long b = (1ULL << ((ld+FracBits)<<1));
				unsigned int c = (1ULL << (ld>>1));
				unsigned long long d = (1ULL << (((ld*6)>>2)+FracBits));
				if (ld&1)
				{
					c *= 23; c >>= 4;
					d *= 22; d >>= 4;
				}
				FixedPoint<Typ,FracBits> x;
				x.Data = div_64_64u(mac_u(a, Data, sq+b),  mac_u(c, Data, d));
				x >>= 2;
				return x;
			}
			else
			{
				FixedPoint<Typ,FracBits> sq = (*this)*(*this);
				unsigned int a = (6U << (ld));
				unsigned int b = (1U << (ld<<1));
				FixedPoint<Typ,FracBits> c = (1U << (ld>>1));
				FixedPoint<Typ,FracBits> d = (1U << ((ld*6)>>2));
				if (ld&1)
				{
					c *= 1.4142136;
					d *= 1.4142136;
				}
				FixedPoint<Typ,FracBits> x = ( sq + a*(*this) + b) / (FixedPoint<Typ,FracBits>(c * (*this)) + d);
				x >>= 2;
				return x;
			}
		}
		else
		{
			ld = Abs(ld);
			FixedPoint<Typ,FracBits> sq = (*this)*(*this);
			FixedPoint<Typ,FracBits> a = 6; a >>= ld;
			FixedPoint<Typ,FracBits> b = 1;  b >>= ld<<1;
			FixedPoint<Typ,FracBits> c = 1;  c >>= ld>>1;
			FixedPoint<Typ,FracBits> d = 1;  d >>= (ld*6)>>2;
			if (ld&1)
			{
				c *= 0.70710578;
				d *= 0.70710578;
			}
			FixedPoint<Typ,FracBits> x = ( sq + a*(*this) + b) / (FixedPoint<Typ,FracBits>(c * (*this)) + d);
			x >>= 2;
			return x;
			}
	}