cuda-samples/Samples/nbody/bodysystemcpu_impl.h

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#include "bodysystemcpu.h"

#include <assert.h>
#include <memory.h>
#include <math.h>
#include <stdlib.h>
#include <stdio.h>
#include <helper_cuda.h>
#include <algorithm>
#include "tipsy.h"

#ifdef OPENMP
#include <omp.h>
#endif

template <typename T>
BodySystemCPU<T>::BodySystemCPU(int numBodies)
    : m_numBodies(numBodies),
      m_bInitialized(false),
      m_force(0),
      m_softeningSquared(.00125f),
      m_damping(0.995f) {
  m_pos = 0;
  m_vel = 0;

  _initialize(numBodies);
}

template <typename T>
BodySystemCPU<T>::~BodySystemCPU() {
  _finalize();
  m_numBodies = 0;
}

template <typename T>
void BodySystemCPU<T>::_initialize(int numBodies) {
  assert(!m_bInitialized);

  m_numBodies = numBodies;

  m_pos = new T[m_numBodies * 4];
  m_vel = new T[m_numBodies * 4];
  m_force = new T[m_numBodies * 3];

  memset(m_pos, 0, m_numBodies * 4 * sizeof(T));
  memset(m_vel, 0, m_numBodies * 4 * sizeof(T));
  memset(m_force, 0, m_numBodies * 3 * sizeof(T));

  m_bInitialized = true;
}

template <typename T>
void BodySystemCPU<T>::_finalize() {
  assert(m_bInitialized);

  delete[] m_pos;
  delete[] m_vel;
  delete[] m_force;

  m_bInitialized = false;
}

template <typename T>
void BodySystemCPU<T>::loadTipsyFile(const std::string &filename) {
  if (m_bInitialized) _finalize();

  vector<typename vec4<T>::Type> positions;
  vector<typename vec4<T>::Type> velocities;
  vector<int> ids;

  int nBodies = 0;
  int nFirst = 0, nSecond = 0, nThird = 0;

  read_tipsy_file(positions, velocities, ids, filename, nBodies, nFirst,
                  nSecond, nThird);

  _initialize(nBodies);

  memcpy(m_pos, &positions[0], sizeof(vec4<T>) * nBodies);
  memcpy(m_vel, &velocities[0], sizeof(vec4<T>) * nBodies);
}

template <typename T>
void BodySystemCPU<T>::update(T deltaTime) {
  assert(m_bInitialized);

  _integrateNBodySystem(deltaTime);

  // std::swap(m_currentRead, m_currentWrite);
}

template <typename T>
T *BodySystemCPU<T>::getArray(BodyArray array) {
  assert(m_bInitialized);

  T *data = 0;

  switch (array) {
    default:
    case BODYSYSTEM_POSITION:
      data = m_pos;
      break;

    case BODYSYSTEM_VELOCITY:
      data = m_vel;
      break;
  }

  return data;
}

template <typename T>
void BodySystemCPU<T>::setArray(BodyArray array, const T *data) {
  assert(m_bInitialized);

  T *target = 0;

  switch (array) {
    default:
    case BODYSYSTEM_POSITION:
      target = m_pos;
      break;

    case BODYSYSTEM_VELOCITY:
      target = m_vel;
      break;
  }

  memcpy(target, data, m_numBodies * 4 * sizeof(T));
}

template <typename T>
T sqrt_T(T x) {
  return sqrt(x);
}

template <>
float sqrt_T<float>(float x) {
  return sqrtf(x);
}

template <typename T>
void bodyBodyInteraction(T accel[3], T posMass0[4], T posMass1[4],
                         T softeningSquared) {
  T r[3];

  // r_01  [3 FLOPS]
  r[0] = posMass1[0] - posMass0[0];
  r[1] = posMass1[1] - posMass0[1];
  r[2] = posMass1[2] - posMass0[2];

  // d^2 + e^2 [6 FLOPS]
  T distSqr = r[0] * r[0] + r[1] * r[1] + r[2] * r[2];
  distSqr += softeningSquared;

  // invDistCube =1/distSqr^(3/2)  [4 FLOPS (2 mul, 1 sqrt, 1 inv)]
  T invDist = (T)1.0 / (T)sqrt((double)distSqr);
  T invDistCube = invDist * invDist * invDist;

  // s = m_j * invDistCube [1 FLOP]
  T s = posMass1[3] * invDistCube;

  // (m_1 * r_01) / (d^2 + e^2)^(3/2)  [6 FLOPS]
  accel[0] += r[0] * s;
  accel[1] += r[1] * s;
  accel[2] += r[2] * s;
}

template <typename T>
void BodySystemCPU<T>::_computeNBodyGravitation() {
#ifdef OPENMP
#pragma omp parallel for
#endif

  for (int i = 0; i < m_numBodies; i++) {
    int indexForce = 3 * i;

    T acc[3] = {0, 0, 0};

    // We unroll this loop 4X for a small performance boost.
    int j = 0;

    while (j < m_numBodies) {
      bodyBodyInteraction<T>(acc, &m_pos[4 * i], &m_pos[4 * j],
                             m_softeningSquared);
      j++;
      bodyBodyInteraction<T>(acc, &m_pos[4 * i], &m_pos[4 * j],
                             m_softeningSquared);
      j++;
      bodyBodyInteraction<T>(acc, &m_pos[4 * i], &m_pos[4 * j],
                             m_softeningSquared);
      j++;
      bodyBodyInteraction<T>(acc, &m_pos[4 * i], &m_pos[4 * j],
                             m_softeningSquared);
      j++;
    }

    m_force[indexForce] = acc[0];
    m_force[indexForce + 1] = acc[1];
    m_force[indexForce + 2] = acc[2];
  }
}

template <typename T>
void BodySystemCPU<T>::_integrateNBodySystem(T deltaTime) {
  _computeNBodyGravitation();

#ifdef OPENMP
#pragma omp parallel for
#endif

  for (int i = 0; i < m_numBodies; ++i) {
    int index = 4 * i;
    int indexForce = 3 * i;

    T pos[3], vel[3], force[3];
    pos[0] = m_pos[index + 0];
    pos[1] = m_pos[index + 1];
    pos[2] = m_pos[index + 2];
    T invMass = m_pos[index + 3];

    vel[0] = m_vel[index + 0];
    vel[1] = m_vel[index + 1];
    vel[2] = m_vel[index + 2];

    force[0] = m_force[indexForce + 0];
    force[1] = m_force[indexForce + 1];
    force[2] = m_force[indexForce + 2];

    // acceleration = force / mass;
    // new velocity = old velocity + acceleration * deltaTime
    vel[0] += (force[0] * invMass) * deltaTime;
    vel[1] += (force[1] * invMass) * deltaTime;
    vel[2] += (force[2] * invMass) * deltaTime;

    vel[0] *= m_damping;
    vel[1] *= m_damping;
    vel[2] *= m_damping;

    // new position = old position + velocity * deltaTime
    pos[0] += vel[0] * deltaTime;
    pos[1] += vel[1] * deltaTime;
    pos[2] += vel[2] * deltaTime;

    m_pos[index + 0] = pos[0];
    m_pos[index + 1] = pos[1];
    m_pos[index + 2] = pos[2];

    m_vel[index + 0] = vel[0];
    m_vel[index + 1] = vel[1];
    m_vel[index + 2] = vel[2];
  }
}