code example
POSIX threads
SSE IA SIMD instructions

#include <pthread.h>
#include <xmmintrin.h>

float *x, *y;
#define PROC (8)
float e_vec[PROC];
int n_thread0, n_thread1;

void *thread1(void *arg) {
  int p = (int)arg;
  int n0 = n_thread0 + (p * (n_thread1-n_thread0)) / PROC;
  int n1 = n_thread0 + ((p+1) * (n_thread1-n_thread0)) / PROC;
  // do computation
  float ve[4] = {0, 0, 0, 0};
  float e = 0;
  for (int i=n0; i<n1; i+=4) {
   float half =.5;
   _mm_store_ps(&x[i],
     _mm_mul_ps(_mm_load1_ps(&half),
       _mm_add_ps(_mm_loadu_ps(&y[i+1]),
         _mm_loadu_ps(&y[i-1]))));
   _mm_store_ps(&ve[0],
     _mm_add_ps(_mm_load_ps(&ve[0]),
       _mm_mul_ps(_mm_load_ps(&y[i]),
         _mm_load_ps(&y[i]))));
  }
  e += ve[0] + ve[1] + ve[2] + ve[3];
  e_vec[p] = e;
  return (void*) 0;
}

int main(int argc, char *argv[]) {
  int n = ...;
  x = new float[n+1];
  y = new float[n+1];

  ... // fill x, y

  pthread_t threads[PROC];
  pthread_attr_t attr;
  pthread_attr_init(&attr);
  n_thread0 = 1;
  n_thread1 = n;
  float e = 0;
  // start threads and wait for termination
  for (int p=0; p<PROC; ++p)
   pthread_create(&threads[p], &attr, thread1, (void *)p);
  for (int p=0; p<PROC; ++p) {
   pthread_join(threads[p], NULL);
   e += e_vec[p];
  }

  ... // output x, e

  delete[] x, y;
  return 0;
}

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