return -(C1 + x*(C2+x*(C3+C4*x)));
return NEG16(C1 + x*(C2+x*(C3+C4*x)));
static inline spx_word16_t spx_cos(spx_word16_t x){   if (x<SPX_PI_2)   {      x *= x;      return C1 + x*(C2+x*(C3+C4*x));   } else {      x = M_PI-x;      x *= x;      return -(C1 + x*(C2+x*(C3+C4*x)));   }}