int ordina( int N, float v[]) {
  int i, j, k=0;
  float separator;
  float dum;
  if (N<2) return 0;
  separator = v[N/2];  
  i=0;
  j=N-1;
  while (j>i) {
    while ( v[i]<separator ) i++;
    while ( v[j]>separator ) j--;
    if (i<j) {
      dum = v[i];
      v[i]= v[j];
      v[j]= dum;
      k++;
      i++;
    }
  } 
  ordina(i,v);
  ordina(N-i,v+i);
  return k;
}