C++ for Scientists - Technische Universität Dresden

170 CHAPTER 5. META-PROGRAMMING
only a sum but in theory it could be tons of them) only return objects with references. The
loop operator= is split into the unrolled at the beginning and the one-by-one completion at the
end:
template
class vector
{
template
vector& operator=(const Src& that)
{
check size(size(that));
unsigned s= my size, sb= s / 4 ∗ 4;
};
}
for (unsigned i= 0; i < sb; i+= 4)
assign()(∗this, that, i);
for (unsigned i= sb; i < s; i++)
data[i]= that[i];
return ∗this;
The assign functor is realized analogous to my axpy ftor:
template
struct assign
{
template
void operator()(U& u, const V& v, unsigned i)
{
u[i+Offset]= v[i+Offset];
assign()(u, v, i);
}
};
template
struct assign
{
template
void operator()(U& u, const V& v, unsigned i) {}
};
Computing the expression above we yield:
Compute time is 1.37 µs.
With this rather simple modification we now accelerated ALL vector expression templates.
In comparison with the previous implementation we lost however the flexibility to costumize
the loop unrolling. The functor assign has two arguments thus allowing for customization. The
problem is the assignment operator. In principle we can define an explicit template argument
there:
template
vector& operator=(const Src& that)
{