Perl_sv_2nv_flags(pTHX_ SV *const sv, const I32 flags)
{
    dVAR;
    if (!sv)
	return 0.0;
    if (SvGMAGICAL(sv) || SvVALID(sv) || isREGEXP(sv)) {
	/* FBMs use the space for SvIVX and SvNVX for other purposes, and use
	   the same flag bit as SVf_IVisUV, so must not let them cache NVs.
	   Regexps have no SvIVX and SvNVX fields.  */
	const char *ptr;
	if (flags & SV_GMAGIC)
	    mg_get(sv);
	if (SvNOKp(sv))
	    return SvNVX(sv);