function normalize$4(out, a) {
    var x = a[0];
    var y = a[1];
    var z = a[2];
    var len = x * x + y * y + z * z;

    if (len > 0) {
      //TODO: evaluate use of glm_invsqrt here?
      len = 1 / Math.sqrt(len);
    }

    out[0] = a[0] * len;
    out[1] = a[1] * len;
    out[2] = a[2] * len;
    return out;
  }
Normalize a vec3

@param {vec3} out the receiving vector
@param {ReadonlyVec3} a vector to normalize
@returns {vec3} out