Comments for the code:
- Block - is a class of one block (8x8 bytes) element.
- _data - array of elements of this block (b)
- bl - array of elements of bl block (a)
- diri - is a Sum(ai*bi)
- d - is a Sum(ai)
- r - is a Sum(bi)
- d2 - is a Sum(ai*ai)
- r2 - is a Sum(bi*bi)
[C++ code] :
BlockDistance Block::Distance( Block *bl )
{
BlockDistance bd;
int diri = std::inner_product(_data, _data + block_size * block_size, &((*bl)[0]), 0);
int d=getR(), r=bl->getR(), d2 = getR2(), r2 = bl->getR2();
int N = block_size*block_size;
if (N*d2-d*d != 0.0)
bd.Factor = (double)(N*diri-d*r)/(double)(N*d2-d*d);
else bd.Factor = 0.0;
bd.Shift = (r-bd.Factor*d)/(double)N;
double ddd = d2 + (bd.Factor * bd.Factor * r2) + N * (bd.Shift * bd.Shift) - 2 * (bd.Factor * diri) - 2* (d * bd.Shift) + 2 * (bd.Factor * bd.Shift * r);
bd.Distance = ddd / N;
return bd;
}
This method also used the following functions. Them calculates Sum(ai) and Sum(ai*ai) and saves calculated value into some cache variable, because these values are used many times.
[C++ code]:
inline int getR()
{
if (!(_calculated_flags & 1))
{
_r = std::accumulate(_data, _data + block_size * block_size, 0);
_calculated_flags ^= 1;
}
return _r;
}
inline int getR2()
{
if (!(_calculated_flags & 2))
{
_r2 = std::inner_product(_data, _data + block_size * block_size, _data, 0);
_calculated_flags ^= 2;
}
return _r2;
}
