/* Need -0.0 for SvNVX to preserve IEEE FP "negative zero" because
   +0.0 + -0.0 => +0.0 but -0.0 + -0.0 => -0.0 */
#  define SvIVX(sv) (0 + ((XPVIV*) SvANY(sv))->xiv_iv)
#  define SvUVX(sv) (0 + ((XPVUV*) SvANY(sv))->xuv_uv)
#  define SvNVX(sv) (-0.0 + ((XPVNV*) SvANY(sv))->xnv_u.xnv_nv)