parallel_programming/openMP/openMp_map.cpp

#include <iostream> // cout
#include <vector>

#include <cstdlib> // srand, rand, atoi
#include <ctime> // time, timespec, clock_gettime
#include <cmath> // pow, sqrt, log


const int RANDOM_MAX = 1000;
const int RANDOM_MIN = 1;


timespec diff(timespec start, timespec end)
{
  timespec temp;
  if ((end.tv_nsec-start.tv_nsec)<0) {
    temp.tv_sec = end.tv_sec-start.tv_sec-1;
    temp.tv_nsec = 1000000000+end.tv_nsec-start.tv_nsec;
  } else {
    temp.tv_sec = end.tv_sec-start.tv_sec;
    temp.tv_nsec = end.tv_nsec-start.tv_nsec;
  }
  return temp;
}


// passing by value and not a reference saves memory read time
float modify(float value)
{
  return 13.37 * pow(sqrt(value), log(value));
}


void openMpMap(std::vector<float>& data,
               const int numberOfThreads,
               const int chunkSize)
{
  size_t i;

#pragma omp parallel for      \
  default(shared) private(i)  \
  schedule(dynamic, chunkSize) \
  num_threads(numberOfThreads)

  for (i = 0; i < data.size(); i++)
    data[i] = modify(data[i]);
}


int main(int argc, char* argv[])
{
  if (argc != 3) {
    std::cout << "Usage: " << argv[0] << " <NUMBER_OF_THREADS> <DATA_SIZE>" << std::endl;
    exit(1);
  }

  const int NUMBER_OF_THREADS = atoi(argv[1]);
  const int DATA_SIZE = atoi(argv[2]);
  const int CHUNK_SIZE = DATA_SIZE / NUMBER_OF_THREADS;

  srand(time(NULL));

  std::vector<float> data(DATA_SIZE);
  for (int i = 0; i < DATA_SIZE; i++)
    data[i] = rand() % RANDOM_MAX + RANDOM_MIN;

  timespec startTime;
  clock_gettime(CLOCK_MONOTONIC, &startTime);

  openMpMap(data, NUMBER_OF_THREADS, CHUNK_SIZE);

  timespec endTime;
  clock_gettime(CLOCK_MONOTONIC, &endTime);
  timespec timeDiff = diff(startTime, endTime);
  std::cout << timeDiff.tv_sec << "." << timeDiff.tv_nsec << std::endl;

  return 0;
}