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platforms/cpu/src/CpuNonbondedForceVec8.cpp
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/* Portions copyright (c) 2006-2013 Stanford University and Simbios.
* Contributors: Pande Group
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject
* to the following conditions:
*
* The above copyright notice and this permission notice shall be included
* in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
* IN NO EVENT SHALL THE AUTHORS, CONTRIBUTORS OR COPYRIGHT HOLDERS BE
* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#include "SimTKOpenMMCommon.h"
#include "SimTKOpenMMUtilities.h"
#include "CpuNonbondedForceVec8.h"
#include "openmm/OpenMMException.h"
#include "openmm/internal/hardware.h"
using namespace std;
using namespace OpenMM;
#ifdef _MSC_VER
// Workaround for a compiler bug in Visual Studio 10. Hopefully we can remove this
// once we move to a later version.
#undef __AVX__
#endif
#ifndef __AVX__
bool isVec8Supported() {
return false;
}
CpuNonbondedForce* createCpuNonbondedForceVec8() {
throw OpenMMException("Internal error: OpenMM was compiled without AVX support");
}
#else
/**
* Check whether 8 component vectors are supported with the current CPU.
*/
bool isVec8Supported() {
// Make sure the CPU supports AVX.
int cpuInfo[4];
cpuid(cpuInfo, 0);
if (cpuInfo[0] >= 1) {
cpuid(cpuInfo, 1);
return ((cpuInfo[2] & ((int) 1 << 28)) != 0);
}
return false;
}
/**
* Factory method to create a CpuNonbondedForceVec8.
*/
CpuNonbondedForce* createCpuNonbondedForceVec8() {
return new CpuNonbondedForceVec8();
}
/**---------------------------------------------------------------------------------------
CpuNonbondedForceVec8 constructor
--------------------------------------------------------------------------------------- */
CpuNonbondedForceVec8::CpuNonbondedForceVec8() {
}
void CpuNonbondedForceVec8::calculateBlockIxn(int blockIndex, float* forces, double* totalEnergy, const fvec4& boxSize, const fvec4& invBoxSize) {
// Load the positions and parameters of the atoms in the block.
const int* blockAtom = &neighborList->getSortedAtoms()[8*blockIndex];
fvec4 blockAtomPosq[8];
fvec8 blockAtomForceX(0.0f), blockAtomForceY(0.0f), blockAtomForceZ(0.0f);
fvec8 blockAtomX, blockAtomY, blockAtomZ, blockAtomCharge;
for (int i = 0; i < 8; i++)
blockAtomPosq[i] = fvec4(posq+4*blockAtom[i]);
transpose(blockAtomPosq[0], blockAtomPosq[1], blockAtomPosq[2], blockAtomPosq[3], blockAtomPosq[4], blockAtomPosq[5], blockAtomPosq[6], blockAtomPosq[7], blockAtomX, blockAtomY, blockAtomZ, blockAtomCharge);
blockAtomCharge *= ONE_4PI_EPS0;
fvec8 blockAtomSigma(atomParameters[blockAtom[0]].first, atomParameters[blockAtom[1]].first, atomParameters[blockAtom[2]].first, atomParameters[blockAtom[3]].first, atomParameters[blockAtom[4]].first, atomParameters[blockAtom[5]].first, atomParameters[blockAtom[6]].first, atomParameters[blockAtom[7]].first);
fvec8 blockAtomEpsilon(atomParameters[blockAtom[0]].second, atomParameters[blockAtom[1]].second, atomParameters[blockAtom[2]].second, atomParameters[blockAtom[3]].second, atomParameters[blockAtom[4]].second, atomParameters[blockAtom[5]].second, atomParameters[blockAtom[6]].second, atomParameters[blockAtom[7]].second);
bool needPeriodic = (periodic && (any(blockAtomX < cutoffDistance) || any(blockAtomY < cutoffDistance) || any(blockAtomZ < cutoffDistance) ||
any(blockAtomX > boxSize[0]-cutoffDistance) || any(blockAtomY > boxSize[1]-cutoffDistance) || any(blockAtomZ > boxSize[2]-cutoffDistance)));
const float invSwitchingInterval = 1/(cutoffDistance-switchingDistance);
// Loop over neighbors for this block.
const vector<int>& neighbors = neighborList->getBlockNeighbors(blockIndex);
const vector<char>& exclusions = neighborList->getBlockExclusions(blockIndex);
for (int i = 0; i < (int) neighbors.size(); i++) {
// Load the next neighbor.
int atom = neighbors[i];
// Compute the distances to the block atoms.
fvec8 dx, dy, dz, r2;
getDeltaR(&posq[4*atom], blockAtomX, blockAtomY, blockAtomZ, dx, dy, dz, r2, needPeriodic, boxSize, invBoxSize);
ivec8 include;
char excl = exclusions[i];
if (excl == 0)
include = -1;
else
include = ivec8(excl&1 ? 0 : -1, excl&2 ? 0 : -1, excl&4 ? 0 : -1, excl&8 ? 0 : -1, excl&16 ? 0 : -1, excl&32 ? 0 : -1, excl&64 ? 0 : -1, excl&128 ? 0 : -1);
include = include & (r2 < cutoffDistance*cutoffDistance);
if (!any(include))
continue; // No interactions to compute.
// Compute the interactions.
fvec8 r = sqrt(r2);
fvec8 inverseR = fvec8(1.0f)/r;
fvec8 energy, dEdR;
float atomEpsilon = atomParameters[atom].second;
if (atomEpsilon != 0.0f) {
fvec8 sig = blockAtomSigma+atomParameters[atom].first;
fvec8 sig2 = inverseR*sig;
sig2 *= sig2;
fvec8 sig6 = sig2*sig2*sig2;
fvec8 epsSig6 = blockAtomEpsilon*atomEpsilon*sig6;
dEdR = epsSig6*(12.0f*sig6 - 6.0f);
energy = epsSig6*(sig6-1.0f);
if (useSwitch) {
fvec8 t = (r>switchingDistance) & ((r-switchingDistance)*invSwitchingInterval);
fvec8 switchValue = 1+t*t*t*(-10.0f+t*(15.0f-t*6.0f));
fvec8 switchDeriv = t*t*(-30.0f+t*(60.0f-t*30.0f))*invSwitchingInterval;
dEdR = switchValue*dEdR - energy*switchDeriv*r;
energy *= switchValue;
}
}
else {
energy = 0.0f;
dEdR = 0.0f;
}
fvec8 chargeProd = blockAtomCharge*posq[4*atom+3];
if (cutoff)
dEdR += chargeProd*(inverseR-2.0f*krf*r2);
else
dEdR += chargeProd*inverseR;
dEdR *= inverseR*inverseR;
// Accumulate energies.
fvec8 one(1.0f);
if (totalEnergy) {
if (cutoff)
energy += chargeProd*(inverseR+krf*r2-crf);
else
energy += chargeProd*inverseR;
energy = blend(0.0f, energy, include);
*totalEnergy += dot8(energy, one);
}
// Accumulate forces.
dEdR = blend(0.0f, dEdR, include);
fvec8 fx = dx*dEdR;
fvec8 fy = dy*dEdR;
fvec8 fz = dz*dEdR;
blockAtomForceX += fx;
blockAtomForceY += fy;
blockAtomForceZ += fz;
float* atomForce = forces+4*atom;
atomForce[0] -= dot8(fx, one);
atomForce[1] -= dot8(fy, one);
atomForce[2] -= dot8(fz, one);
}
// Record the forces on the block atoms.
fvec4 f[8];
transpose(blockAtomForceX, blockAtomForceY, blockAtomForceZ, 0.0f, f[0], f[1], f[2], f[3], f[4], f[5], f[6], f[7]);
for (int j = 0; j < 8; j++)
(fvec4(forces+4*blockAtom[j])+f[j]).store(forces+4*blockAtom[j]);
}
void CpuNonbondedForceVec8::calculateBlockEwaldIxn(int blockIndex, float* forces, double* totalEnergy, const fvec4& boxSize, const fvec4& invBoxSize) {
// Load the positions and parameters of the atoms in the block.
const int* blockAtom = &neighborList->getSortedAtoms()[8*blockIndex];
fvec4 blockAtomPosq[8];
fvec8 blockAtomForceX(0.0f), blockAtomForceY(0.0f), blockAtomForceZ(0.0f);
fvec8 blockAtomX, blockAtomY, blockAtomZ, blockAtomCharge;
for (int i = 0; i < 8; i++)
blockAtomPosq[i] = fvec4(posq+4*blockAtom[i]);
transpose(blockAtomPosq[0], blockAtomPosq[1], blockAtomPosq[2], blockAtomPosq[3], blockAtomPosq[4], blockAtomPosq[5], blockAtomPosq[6], blockAtomPosq[7], blockAtomX, blockAtomY, blockAtomZ, blockAtomCharge);
blockAtomCharge *= ONE_4PI_EPS0;
fvec8 blockAtomSigma(atomParameters[blockAtom[0]].first, atomParameters[blockAtom[1]].first, atomParameters[blockAtom[2]].first, atomParameters[blockAtom[3]].first, atomParameters[blockAtom[4]].first, atomParameters[blockAtom[5]].first, atomParameters[blockAtom[6]].first, atomParameters[blockAtom[7]].first);
fvec8 blockAtomEpsilon(atomParameters[blockAtom[0]].second, atomParameters[blockAtom[1]].second, atomParameters[blockAtom[2]].second, atomParameters[blockAtom[3]].second, atomParameters[blockAtom[4]].second, atomParameters[blockAtom[5]].second, atomParameters[blockAtom[6]].second, atomParameters[blockAtom[7]].second);
bool needPeriodic = (periodic && (any(blockAtomX < cutoffDistance) || any(blockAtomY < cutoffDistance) || any(blockAtomZ < cutoffDistance) ||
any(blockAtomX > boxSize[0]-cutoffDistance) || any(blockAtomY > boxSize[1]-cutoffDistance) || any(blockAtomZ > boxSize[2]-cutoffDistance)));
const float invSwitchingInterval = 1/(cutoffDistance-switchingDistance);
// Loop over neighbors for this block.
const vector<int>& neighbors = neighborList->getBlockNeighbors(blockIndex);
const vector<char>& exclusions = neighborList->getBlockExclusions(blockIndex);
for (int i = 0; i < (int) neighbors.size(); i++) {
// Load the next neighbor.
int atom = neighbors[i];
// Compute the distances to the block atoms.
fvec8 dx, dy, dz, r2;
getDeltaR(&posq[4*atom], blockAtomX, blockAtomY, blockAtomZ, dx, dy, dz, r2, needPeriodic, boxSize, invBoxSize);
ivec8 include;
char excl = exclusions[i];
if (excl == 0)
include = -1;
else
include = ivec8(excl&1 ? 0 : -1, excl&2 ? 0 : -1, excl&4 ? 0 : -1, excl&8 ? 0 : -1, excl&16 ? 0 : -1, excl&32 ? 0 : -1, excl&64 ? 0 : -1, excl&128 ? 0 : -1);
include = include & (r2 < cutoffDistance*cutoffDistance);
if (!any(include))
continue; // No interactions to compute.
// Compute the interactions.
fvec8 r = sqrt(r2);
fvec8 inverseR = fvec8(1.0f)/r;
fvec8 energy, dEdR;
float atomEpsilon = atomParameters[atom].second;
if (atomEpsilon != 0.0f) {
fvec8 sig = blockAtomSigma+atomParameters[atom].first;
fvec8 sig2 = inverseR*sig;
sig2 *= sig2;
fvec8 sig6 = sig2*sig2*sig2;
fvec8 epsSig6 = blockAtomEpsilon*atomEpsilon*sig6;
dEdR = epsSig6*(12.0f*sig6 - 6.0f);
energy = epsSig6*(sig6-1.0f);
if (useSwitch) {
fvec8 t = (r>switchingDistance) & ((r-switchingDistance)*invSwitchingInterval);
fvec8 switchValue = 1+t*t*t*(-10.0f+t*(15.0f-t*6.0f));
fvec8 switchDeriv = t*t*(-30.0f+t*(60.0f-t*30.0f))*invSwitchingInterval;
dEdR = switchValue*dEdR - energy*switchDeriv*r;
energy *= switchValue;
}
}
else {
energy = 0.0f;
dEdR = 0.0f;
}
fvec8 chargeProd = blockAtomCharge*posq[4*atom+3];
dEdR += chargeProd*inverseR*ewaldScaleFunction(r);
dEdR *= inverseR*inverseR;
// Accumulate energies.
fvec8 one(1.0f);
if (totalEnergy) {
energy += chargeProd*inverseR*erfcApprox(alphaEwald*r);
energy = blend(0.0f, energy, include);
*totalEnergy += dot8(energy, one);
}
// Accumulate forces.
dEdR = blend(0.0f, dEdR, include);
fvec8 fx = dx*dEdR;
fvec8 fy = dy*dEdR;
fvec8 fz = dz*dEdR;
blockAtomForceX += fx;
blockAtomForceY += fy;
blockAtomForceZ += fz;
float* atomForce = forces+4*atom;
atomForce[0] -= dot8(fx, one);
atomForce[1] -= dot8(fy, one);
atomForce[2] -= dot8(fz, one);
}
// Record the forces on the block atoms.
fvec4 f[8];
transpose(blockAtomForceX, blockAtomForceY, blockAtomForceZ, 0.0f, f[0], f[1], f[2], f[3], f[4], f[5], f[6], f[7]);
for (int j = 0; j < 8; j++)
(fvec4(forces+4*blockAtom[j])+f[j]).store(forces+4*blockAtom[j]);
}
void CpuNonbondedForceVec8::getDeltaR(const float* posI, const fvec8& x, const fvec8& y, const fvec8& z, fvec8& dx, fvec8& dy, fvec8& dz, fvec8& r2, bool periodic, const fvec4& boxSize, const fvec4& invBoxSize) const {
dx = x-posI[0];
dy = y-posI[1];
dz = z-posI[2];
if (periodic) {
dx -= round(dx*invBoxSize[0])*boxSize[0];
dy -= round(dy*invBoxSize[1])*boxSize[1];
dz -= round(dz*invBoxSize[2])*boxSize[2];
}
r2 = dx*dx + dy*dy + dz*dz;
}
fvec8 CpuNonbondedForceVec8::erfcApprox(const fvec8& x) {
// This approximation for erfc is from Abramowitz and Stegun (1964) p. 299. They cite the following as
// the original source: C. Hastings, Jr., Approximations for Digital Computers (1955). It has a maximum
// error of 3e-7.
fvec8 t = 1.0f+(0.0705230784f+(0.0422820123f+(0.0092705272f+(0.0001520143f+(0.0002765672f+0.0000430638f*x)*x)*x)*x)*x)*x;
t *= t;
t *= t;
t *= t;
return 1.0f/(t*t);
}
fvec8 CpuNonbondedForceVec8::ewaldScaleFunction(const fvec8& x) {
// Compute the tabulated Ewald scale factor: erfc(alpha*r) + 2*alpha*r*exp(-alpha*alpha*r*r)/sqrt(PI)
fvec8 x1 = x*ewaldDXInv;
ivec8 index = min(floor(x1), NUM_TABLE_POINTS);
fvec8 coeff2 = x1-index;
fvec8 coeff1 = 1.0f-coeff2;
ivec4 indexLower = index.lowerVec();
ivec4 indexUpper = index.upperVec();
fvec4 t1(&ewaldScaleTable[indexLower[0]]);
fvec4 t2(&ewaldScaleTable[indexLower[1]]);
fvec4 t3(&ewaldScaleTable[indexLower[2]]);
fvec4 t4(&ewaldScaleTable[indexLower[3]]);
fvec4 t5(&ewaldScaleTable[indexUpper[0]]);
fvec4 t6(&ewaldScaleTable[indexUpper[1]]);
fvec4 t7(&ewaldScaleTable[indexUpper[2]]);
fvec4 t8(&ewaldScaleTable[indexUpper[3]]);
fvec8 s1, s2, s3, s4;
transpose(t1, t2, t3, t4, t5, t6, t7, t8, s1, s2, s3, s4);
return coeff1*s1 + coeff2*s2;
}
#endif
/* Portions copyright (c) 2006-2013 Stanford University and Simbios.
* Contributors: Pande Group
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject
* to the following conditions:
*
* The above copyright notice and this permission notice shall be included
* in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
* IN NO EVENT SHALL THE AUTHORS, CONTRIBUTORS OR COPYRIGHT HOLDERS BE
* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#include "SimTKOpenMMCommon.h"
#include "SimTKOpenMMUtilities.h"
#include "CpuNonbondedForceVec8.h"
#include "openmm/OpenMMException.h"
#include "openmm/internal/hardware.h"
using namespace std;
using namespace OpenMM;
#ifdef _MSC_VER
// Workaround for a compiler bug in Visual Studio 10. Hopefully we can remove this
// once we move to a later version.
#undef __AVX__
#endif
#ifndef __AVX__
bool isVec8Supported() {
return false;
}
CpuNonbondedForce* createCpuNonbondedForceVec8() {
throw OpenMMException("Internal error: OpenMM was compiled without AVX support");
}
#else
/**
* Check whether 8 component vectors are supported with the current CPU.
*/
bool isVec8Supported() {
// Make sure the CPU supports AVX.
int cpuInfo[4];
cpuid(cpuInfo, 0);
if (cpuInfo[0] >= 1) {
cpuid(cpuInfo, 1);
return ((cpuInfo[2] & ((int) 1 << 28)) != 0);
}
return false;
}
/**
* Factory method to create a CpuNonbondedForceVec8.
*/
CpuNonbondedForce* createCpuNonbondedForceVec8() {
return new CpuNonbondedForceVec8();
}
/**---------------------------------------------------------------------------------------
CpuNonbondedForceVec8 constructor
--------------------------------------------------------------------------------------- */
CpuNonbondedForceVec8::CpuNonbondedForceVec8() {
}
void CpuNonbondedForceVec8::calculateBlockIxn(int blockIndex, float* forces, double* totalEnergy, const fvec4& boxSize, const fvec4& invBoxSize) {
// Load the positions and parameters of the atoms in the block.
const int* blockAtom = &neighborList->getSortedAtoms()[8*blockIndex];
fvec4 blockAtomPosq[8];
fvec8 blockAtomForceX(0.0f), blockAtomForceY(0.0f), blockAtomForceZ(0.0f);
fvec8 blockAtomX, blockAtomY, blockAtomZ, blockAtomCharge;
for (int i = 0; i < 8; i++)
blockAtomPosq[i] = fvec4(posq+4*blockAtom[i]);
transpose(blockAtomPosq[0], blockAtomPosq[1], blockAtomPosq[2], blockAtomPosq[3], blockAtomPosq[4], blockAtomPosq[5], blockAtomPosq[6], blockAtomPosq[7], blockAtomX, blockAtomY, blockAtomZ, blockAtomCharge);
blockAtomCharge *= ONE_4PI_EPS0;
fvec8 blockAtomSigma(atomParameters[blockAtom[0]].first, atomParameters[blockAtom[1]].first, atomParameters[blockAtom[2]].first, atomParameters[blockAtom[3]].first, atomParameters[blockAtom[4]].first, atomParameters[blockAtom[5]].first, atomParameters[blockAtom[6]].first, atomParameters[blockAtom[7]].first);
fvec8 blockAtomEpsilon(atomParameters[blockAtom[0]].second, atomParameters[blockAtom[1]].second, atomParameters[blockAtom[2]].second, atomParameters[blockAtom[3]].second, atomParameters[blockAtom[4]].second, atomParameters[blockAtom[5]].second, atomParameters[blockAtom[6]].second, atomParameters[blockAtom[7]].second);
bool needPeriodic = (periodic && (any(blockAtomX < cutoffDistance) || any(blockAtomY < cutoffDistance) || any(blockAtomZ < cutoffDistance) ||
any(blockAtomX > boxSize[0]-cutoffDistance) || any(blockAtomY > boxSize[1]-cutoffDistance) || any(blockAtomZ > boxSize[2]-cutoffDistance)));
const float invSwitchingInterval = 1/(cutoffDistance-switchingDistance);
// Loop over neighbors for this block.
const vector<int>& neighbors = neighborList->getBlockNeighbors(blockIndex);
const vector<char>& exclusions = neighborList->getBlockExclusions(blockIndex);
for (int i = 0; i < (int) neighbors.size(); i++) {
// Load the next neighbor.
int atom = neighbors[i];
// Compute the distances to the block atoms.
fvec8 dx, dy, dz, r2;
getDeltaR(&posq[4*atom], blockAtomX, blockAtomY, blockAtomZ, dx, dy, dz, r2, needPeriodic, boxSize, invBoxSize);
ivec8 include;
char excl = exclusions[i];
if (excl == 0)
include = -1;
else
include = ivec8(excl&1 ? 0 : -1, excl&2 ? 0 : -1, excl&4 ? 0 : -1, excl&8 ? 0 : -1, excl&16 ? 0 : -1, excl&32 ? 0 : -1, excl&64 ? 0 : -1, excl&128 ? 0 : -1);
include = include & (r2 < cutoffDistance*cutoffDistance);
if (!any(include))
continue; // No interactions to compute.
// Compute the interactions.
fvec8 r = sqrt(r2);
fvec8 inverseR = fvec8(1.0f)/r;
fvec8 energy, dEdR;
float atomEpsilon = atomParameters[atom].second;
if (atomEpsilon != 0.0f) {
fvec8 sig = blockAtomSigma+atomParameters[atom].first;
fvec8 sig2 = inverseR*sig;
sig2 *= sig2;
fvec8 sig6 = sig2*sig2*sig2;
fvec8 epsSig6 = blockAtomEpsilon*atomEpsilon*sig6;
dEdR = epsSig6*(12.0f*sig6 - 6.0f);
energy = epsSig6*(sig6-1.0f);
if (useSwitch) {
fvec8 t = (r>switchingDistance) & ((r-switchingDistance)*invSwitchingInterval);
fvec8 switchValue = 1+t*t*t*(-10.0f+t*(15.0f-t*6.0f));
fvec8 switchDeriv = t*t*(-30.0f+t*(60.0f-t*30.0f))*invSwitchingInterval;
dEdR = switchValue*dEdR - energy*switchDeriv*r;
energy *= switchValue;
}
}
else {
energy = 0.0f;
dEdR = 0.0f;
}
fvec8 chargeProd = blockAtomCharge*posq[4*atom+3];
if (cutoff)
dEdR += chargeProd*(inverseR-2.0f*krf*r2);
else
dEdR += chargeProd*inverseR;
dEdR *= inverseR*inverseR;
// Accumulate energies.
fvec8 one(1.0f);
if (totalEnergy) {
if (cutoff)
energy += chargeProd*(inverseR+krf*r2-crf);
else
energy += chargeProd*inverseR;
energy = blend(0.0f, energy, include);
*totalEnergy += dot8(energy, one);
}
// Accumulate forces.
dEdR = blend(0.0f, dEdR, include);
fvec8 fx = dx*dEdR;
fvec8 fy = dy*dEdR;
fvec8 fz = dz*dEdR;
blockAtomForceX += fx;
blockAtomForceY += fy;
blockAtomForceZ += fz;
float* atomForce = forces+4*atom;
atomForce[0] -= dot8(fx, one);
atomForce[1] -= dot8(fy, one);
atomForce[2] -= dot8(fz, one);
}
// Record the forces on the block atoms.
fvec4 f[8];
transpose(blockAtomForceX, blockAtomForceY, blockAtomForceZ, 0.0f, f[0], f[1], f[2], f[3], f[4], f[5], f[6], f[7]);
for (int j = 0; j < 8; j++)
(fvec4(forces+4*blockAtom[j])+f[j]).store(forces+4*blockAtom[j]);
}
void CpuNonbondedForceVec8::calculateBlockEwaldIxn(int blockIndex, float* forces, double* totalEnergy, const fvec4& boxSize, const fvec4& invBoxSize) {
// Load the positions and parameters of the atoms in the block.
const int* blockAtom = &neighborList->getSortedAtoms()[8*blockIndex];
fvec4 blockAtomPosq[8];
fvec8 blockAtomForceX(0.0f), blockAtomForceY(0.0f), blockAtomForceZ(0.0f);
fvec8 blockAtomX, blockAtomY, blockAtomZ, blockAtomCharge;
for (int i = 0; i < 8; i++)
blockAtomPosq[i] = fvec4(posq+4*blockAtom[i]);
transpose(blockAtomPosq[0], blockAtomPosq[1], blockAtomPosq[2], blockAtomPosq[3], blockAtomPosq[4], blockAtomPosq[5], blockAtomPosq[6], blockAtomPosq[7], blockAtomX, blockAtomY, blockAtomZ, blockAtomCharge);
blockAtomCharge *= ONE_4PI_EPS0;
fvec8 blockAtomSigma(atomParameters[blockAtom[0]].first, atomParameters[blockAtom[1]].first, atomParameters[blockAtom[2]].first, atomParameters[blockAtom[3]].first, atomParameters[blockAtom[4]].first, atomParameters[blockAtom[5]].first, atomParameters[blockAtom[6]].first, atomParameters[blockAtom[7]].first);
fvec8 blockAtomEpsilon(atomParameters[blockAtom[0]].second, atomParameters[blockAtom[1]].second, atomParameters[blockAtom[2]].second, atomParameters[blockAtom[3]].second, atomParameters[blockAtom[4]].second, atomParameters[blockAtom[5]].second, atomParameters[blockAtom[6]].second, atomParameters[blockAtom[7]].second);
bool needPeriodic = (periodic && (any(blockAtomX < cutoffDistance) || any(blockAtomY < cutoffDistance) || any(blockAtomZ < cutoffDistance) ||
any(blockAtomX > boxSize[0]-cutoffDistance) || any(blockAtomY > boxSize[1]-cutoffDistance) || any(blockAtomZ > boxSize[2]-cutoffDistance)));
const float invSwitchingInterval = 1/(cutoffDistance-switchingDistance);
// Loop over neighbors for this block.
const vector<int>& neighbors = neighborList->getBlockNeighbors(blockIndex);
const vector<char>& exclusions = neighborList->getBlockExclusions(blockIndex);
for (int i = 0; i < (int) neighbors.size(); i++) {
// Load the next neighbor.
int atom = neighbors[i];
// Compute the distances to the block atoms.
fvec8 dx, dy, dz, r2;
getDeltaR(&posq[4*atom], blockAtomX, blockAtomY, blockAtomZ, dx, dy, dz, r2, needPeriodic, boxSize, invBoxSize);
ivec8 include;
char excl = exclusions[i];
if (excl == 0)
include = -1;
else
include = ivec8(excl&1 ? 0 : -1, excl&2 ? 0 : -1, excl&4 ? 0 : -1, excl&8 ? 0 : -1, excl&16 ? 0 : -1, excl&32 ? 0 : -1, excl&64 ? 0 : -1, excl&128 ? 0 : -1);
include = include & (r2 < cutoffDistance*cutoffDistance);
if (!any(include))
continue; // No interactions to compute.
// Compute the interactions.
fvec8 r = sqrt(r2);
fvec8 inverseR = fvec8(1.0f)/r;
fvec8 energy, dEdR;
float atomEpsilon = atomParameters[atom].second;
if (atomEpsilon != 0.0f) {
fvec8 sig = blockAtomSigma+atomParameters[atom].first;
fvec8 sig2 = inverseR*sig;
sig2 *= sig2;
fvec8 sig6 = sig2*sig2*sig2;
fvec8 epsSig6 = blockAtomEpsilon*atomEpsilon*sig6;
dEdR = epsSig6*(12.0f*sig6 - 6.0f);
energy = epsSig6*(sig6-1.0f);
if (useSwitch) {
fvec8 t = (r>switchingDistance) & ((r-switchingDistance)*invSwitchingInterval);
fvec8 switchValue = 1+t*t*t*(-10.0f+t*(15.0f-t*6.0f));
fvec8 switchDeriv = t*t*(-30.0f+t*(60.0f-t*30.0f))*invSwitchingInterval;
dEdR = switchValue*dEdR - energy*switchDeriv*r;
energy *= switchValue;
}
}
else {
energy = 0.0f;
dEdR = 0.0f;
}
fvec8 chargeProd = blockAtomCharge*posq[4*atom+3];
dEdR += chargeProd*inverseR*ewaldScaleFunction(r);
dEdR *= inverseR*inverseR;
// Accumulate energies.
fvec8 one(1.0f);
if (totalEnergy) {
energy += chargeProd*inverseR*erfcApprox(alphaEwald*r);
energy = blend(0.0f, energy, include);
*totalEnergy += dot8(energy, one);
}
// Accumulate forces.
dEdR = blend(0.0f, dEdR, include);
fvec8 fx = dx*dEdR;
fvec8 fy = dy*dEdR;
fvec8 fz = dz*dEdR;
blockAtomForceX += fx;
blockAtomForceY += fy;
blockAtomForceZ += fz;
float* atomForce = forces+4*atom;
atomForce[0] -= dot8(fx, one);
atomForce[1] -= dot8(fy, one);
atomForce[2] -= dot8(fz, one);
}
// Record the forces on the block atoms.
fvec4 f[8];
transpose(blockAtomForceX, blockAtomForceY, blockAtomForceZ, 0.0f, f[0], f[1], f[2], f[3], f[4], f[5], f[6], f[7]);
for (int j = 0; j < 8; j++)
(fvec4(forces+4*blockAtom[j])+f[j]).store(forces+4*blockAtom[j]);
}
void CpuNonbondedForceVec8::getDeltaR(const float* posI, const fvec8& x, const fvec8& y, const fvec8& z, fvec8& dx, fvec8& dy, fvec8& dz, fvec8& r2, bool periodic, const fvec4& boxSize, const fvec4& invBoxSize) const {
dx = x-posI[0];
dy = y-posI[1];
dz = z-posI[2];
if (periodic) {
dx -= round(dx*invBoxSize[0])*boxSize[0];
dy -= round(dy*invBoxSize[1])*boxSize[1];
dz -= round(dz*invBoxSize[2])*boxSize[2];
}
r2 = dx*dx + dy*dy + dz*dz;
}
fvec8 CpuNonbondedForceVec8::erfcApprox(const fvec8& x) {
// This approximation for erfc is from Abramowitz and Stegun (1964) p. 299. They cite the following as
// the original source: C. Hastings, Jr., Approximations for Digital Computers (1955). It has a maximum
// error of 3e-7.
fvec8 t = 1.0f+(0.0705230784f+(0.0422820123f+(0.0092705272f+(0.0001520143f+(0.0002765672f+0.0000430638f*x)*x)*x)*x)*x)*x;
t *= t;
t *= t;
t *= t;
return 1.0f/(t*t);
}
fvec8 CpuNonbondedForceVec8::ewaldScaleFunction(const fvec8& x) {
// Compute the tabulated Ewald scale factor: erfc(alpha*r) + 2*alpha*r*exp(-alpha*alpha*r*r)/sqrt(PI)
fvec8 x1 = x*ewaldDXInv;
ivec8 index = min(floor(x1), NUM_TABLE_POINTS);
fvec8 coeff2 = x1-index;
fvec8 coeff1 = 1.0f-coeff2;
ivec4 indexLower = index.lowerVec();
ivec4 indexUpper = index.upperVec();
fvec4 t1(&ewaldScaleTable[indexLower[0]]);
fvec4 t2(&ewaldScaleTable[indexLower[1]]);
fvec4 t3(&ewaldScaleTable[indexLower[2]]);
fvec4 t4(&ewaldScaleTable[indexLower[3]]);
fvec4 t5(&ewaldScaleTable[indexUpper[0]]);
fvec4 t6(&ewaldScaleTable[indexUpper[1]]);
fvec4 t7(&ewaldScaleTable[indexUpper[2]]);
fvec4 t8(&ewaldScaleTable[indexUpper[3]]);
fvec8 s1, s2, s3, s4;
transpose(t1, t2, t3, t4, t5, t6, t7, t8, s1, s2, s3, s4);
return coeff1*s1 + coeff2*s2;
}
#endif
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