Random points on sphere

//randomize vectors
const double range = 1.;
for (int i = 0; i != NUM_VECTORS; ++i){
   D3 &v = vectors[i];
   double x;
   do{
      x = v.x = 2*range * rand() / RAND_MAX - range;
      v.y = 2*range * rand() / RAND_MAX - range;
      v.z = 2*range * rand() / RAND_MAX - range;
      normalize(v);
   }while(x/v.x > 1);
}