double Atomtype::CalcPE(int frame_i, const Trajectory &trj, const coordinates &rand_xyz, const cubicbox_m256 &box, double vol) const
{
float pe = 0.0;
int atom_i = 0;
/* BEGIN SIMD SECTION */
// This performs the exact same calculation after the SIMD section
// but doing it on 8 atoms at a time using SIMD instructions.
coordinates8 rand_xyz8(rand_xyz), atom_xyz;
__m256 r2_8, mask, r6, ri6, pe_tmp;
__m256 pe_sum = _mm256_setzero_ps();
float result[n] __attribute__((aligned (16)));
for (; atom_i < this->n-8; atom_i+=8)
{
atom_xyz = trj.GetXYZ8(frame_i, this->name, atom_i);
r2_8 = distance2(atom_xyz, rand_xyz8, box);
mask = _mm256_cmp_ps(r2_8, rcut2_8, _CMP_LT_OS);
r6 = _mm256_and_ps(mask, _mm256_mul_ps(_mm256_mul_ps(r2_8, r2_8), r2_8));
ri6 = _mm256_and_ps(mask, _mm256_rcp_ps(r6));
pe_tmp = _mm256_and_ps(mask, _mm256_mul_ps(ri6, _mm256_sub_ps(_mm256_mul_ps(c12_8, ri6), c6_8)));
pe_sum = _mm256_add_ps(pe_tmp, pe_sum);
}
_mm256_store_ps(result, pe_sum);
for (int i = 0; i < 8; i++)
{
pe += result[i];
}
/* END SIMD SECTION */
for (; atom_i < this->n; atom_i++)
{
coordinates atom_xyz = trj.GetXYZ(frame_i, this->name, atom_i);
float r2 = distance2(atom_xyz, rand_xyz, cubicbox(box));
if (r2 < this->rcut2)
{
float ri6 = 1.0/(pow(r2,3));
pe += ri6*(this->c12*ri6 - this->c6);
}
}
pe += this->n/vol * this->tail_factor;;
return pe;
}
