function cross$2(out, a, b) {
    var ax = a[0],
        ay = a[1],
        az = a[2];
    var bx = b[0],
        by = b[1],
        bz = b[2];
    out[0] = ay * bz - az * by;
    out[1] = az * bx - ax * bz;
    out[2] = ax * by - ay * bx;
    return out;
  }
Computes the cross product of two vec3's

@param {vec3} out the receiving vector
@param {ReadonlyVec3} a the first operand
@param {ReadonlyVec3} b the second operand
@returns {vec3} out