I'm trying to vectorize the inner `for` of this function:
void SIFTDescriptor::samplePatch(float *vec)
{
for (int r = 0; r < par.patchSize; ++r)
{
const int br0 = par.spatialBins * bin0[r]; const float wr0 = w0[r];
const int br1 = par.spatialBins * bin1[r]; const float wr1 = w1[r];
for (int c = 0; c < par.patchSize; ++c)
{
const float val = mask.at<float>(r,c) * grad.at<float>(r,c);
const int bc0 = bin0[c];
const float wc0 = w0[c]*val;
const int bc1 = bin1[c];
const float wc1 = w1[c]*val;
// ori from atan2 is in range <-pi,pi> so add 2*pi to be surely above zero
const float o = float(par.orientationBins)*(ori.at<float>(r,c) + 2*M_PI)/(2*M_PI);
int bo0 = (int)o;
const float wo1 = o - bo0;
bo0 %= par.orientationBins;
int bo1 = (bo0+1) % par.orientationBins;
const float wo0 = 1.0f - wo1;
// add to corresponding 8 vec...
if (wr0*wc0>0) {
vec[br0+bc0+bo0] += wr0*wc0 * wo0;
vec[br0+bc0+bo1] += wr0*wc0 * wo1;
}
if (wr0*wc1>0) {
vec[br0+bc1+bo0] += wr0*wc1 * wo0;
vec[br0+bc1+bo1] += wr0*wc1 * wo1;
}
if (wr1*wc0>0) {
vec[br1+bc0+bo0] += wr1*wc0 * wo0;
vec[br1+bc0+bo1] += wr1*wc0 * wo1;
}
if (wr1*wc0>0) {
vec[br1+bc1+bo0] += wr1*wc0 * wo0;
vec[br1+bc1+bo1] += wr1*wc0 * wo1;
}
}
}
}However, Intel Advisor tells me that there are two Read-After-Write dependencies in:
vec[br0+bc0+bo0] += wr0*wc0 * wo0;
And:
vec[br1+bc0+bo0] += wr1*wc0 * wo0;
How can I solve them? This is the first time that I try to solve such a dependency and I'm struggling a little bit...