void vector3d_normalize(T* v){
T R;
R = vector3d_modulus(v);
v[0] /= R;
v[1] /= R;
v[2] /= R;
}
//convert vector to a vector with same direction and modulus 1
void vector3d_normalize(float* vector){
float R;
R = vector3d_modulus(vector);
vector[0] /= R;
vector[1] /= R;
vector[2] /= R;
}
void MMA8451::update_stillness(const float *result){
float cross[3];
float filtered[3];
float modulus_cross;
float modulus_delta;
uint32_t i = 0;
/* update array of filters */
for (i=0; i<3; i++)
filtered[i] = abeta[i].update(result[i], *still_flen);
/* calculate differences between vectors */
vector3d_cross(result, filtered, cross);
modulus_cross = vector3d_modulus(cross);
modulus_delta = vector3d_modulus(result) - vector3d_modulus(filtered);
if ((fabsf(modulus_delta) > *still_thr) || (fabsf(modulus_cross) > *still_thr))
immobile = false;
}