while (read_from_file(&newzip, &newlat, &newlon)) {
    mydist = great_circle_distance(newlat,newlon,origlat,origlon);
    if (mydist < 25)
    {
      // do stuff to add it to file
    }
    if (mydist < 50)
    {
      ...
    }
    ...
  }

##</code><code>##

  float dist1cosine = cos(25.0 / EARTH_RADIUS);
  float dist2cosine = cos(50.0 / EARTH_RADIUS);
  float dist3cosine = cos(75.0 / EARTH_RADIUS);
  while (read_from_file(&newzip, &newlat, &newlon)) {
    mydistcos = great_circle_distance_cosine(newlat,newlon,
                                             origlat,origlon);
    if (mydistcos >= dist1cosine)
    {
      // do stuff to add it to file
    }
    if (mydistcos >= dist2cosine)
    {
      ...
    }
    ...
  }

##</code><code>##

   static inline float great_circle_distance_cosine(float lat1,
                                             float long1,
                                             float lat2,
                                             float long2) {
           float delta_long, temp1, temp2, delta_lat;

           delta_lat = lat2 - lat1;
           delta_long = long2 - long1;

           temp1 = sin(lat1) * sin(lat2);

           temp2 = cos(delta_lat);
           temp2 -= temp1;
           temp2 *= cos(delta_long);

         /* result is cos(lat1) cos(lat2) [ cos(lon1 - lon2) ] + 
                      sin(lat1) sin(lat2) */
           return (temp1 + temp2);
   }