Optimizing away

Follow-up on Improving performance…  and Genetic Programming: Evolution of Mona Lisa.
I just tested that I can optimize this loop:

unchecked
{
    unsafe
    {
        fixed ( Pixel* psourcePixels = sourcePixels )
        {
            Pixel* p1 = (Pixel*)bd.Scan0.ToPointer();
            Pixel* p2 = psourcePixels;
            for ( int i = sourcePixels.Length ; i > 0 ; i--, p1++, p2++ )
            {
                int r = p1->R - p2->R;
                int g = p1->G - p2->G;
                int b = p1->B - p2->B;
                error += r * r + g * g + b * b;
            }
        }
    }
}

so that it runs even 60% faster. Don’t dare to tell you how, however.

EDIT: Continued here Ekeforshus

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