void
constant(sv)
    PREINIT:
#ifdef dXSTARG
	dXSTARG; /* Faster if we have it.  */
#else
	dTARGET;
#endif
	STRLEN		len;
        int		type;
	IV		iv;
	/* NV		nv;	Uncomment this if you need to return NVs */
	/* const char	*pv;	Uncomment this if you need to return PVs */
    INPUT:
	SV *		sv;
        const char *	s = SvPV(sv, len);
    PPCODE:
        /* Change this to constant(aTHX_ s, len, &iv, &nv);
           if you need to return both NVs and IVs */
	type = constant(aTHX_ s, len, &iv);
      /* Return 1 or 2 items. First is error message, or undef if no error.
           Second, if present, is found value */
        switch (type) {
        case PERL_constant_NOTFOUND:
          sv =
	    sv_2mortal(newSVpvf("%s is not a valid PDL::IO::Image macro", s));
          PUSHs(sv);
          break;
        case PERL_constant_NOTDEF:
          sv = sv_2mortal(newSVpvf(
	    "Your vendor has not defined PDL::IO::Image macro %s, used",
				   s));
          PUSHs(sv);
          break;
        case PERL_constant_ISIV:
          EXTEND(SP, 1);
          PUSHs(&PL_sv_undef);
          PUSHi(iv);
          break;
	/* Uncomment this if you need to return NOs
        case PERL_constant_ISNO:
          EXTEND(SP, 1);
          PUSHs(&PL_sv_undef);
          PUSHs(&PL_sv_no);
          break; */
	/* Uncomment this if you need to return NVs
        case PERL_constant_ISNV:
          EXTEND(SP, 1);
          PUSHs(&PL_sv_undef);
          PUSHn(nv);
          break; */
	/* Uncomment this if you need to return PVs
        case PERL_constant_ISPV:
          EXTEND(SP, 1);
          PUSHs(&PL_sv_undef);
          PUSHp(pv, strlen(pv));
          break; */
	/* Uncomment this if you need to return PVNs
        case PERL_constant_ISPVN:
          EXTEND(SP, 1);
          PUSHs(&PL_sv_undef);
          PUSHp(pv, iv);
          break; */
	/* Uncomment this if you need to return SVs
        case PERL_constant_ISSV:
          EXTEND(SP, 1);
          PUSHs(&PL_sv_undef);
          PUSHs(sv);
          break; */
	/* Uncomment this if you need to return UNDEFs
        case PERL_constant_ISUNDEF:
          break; */
	/* Uncomment this if you need to return UVs
        case PERL_constant_ISUV:
          EXTEND(SP, 1);
          PUSHs(&PL_sv_undef);
          PUSHu((UV)iv);
          break; */
	/* Uncomment this if you need to return YESs
        case PERL_constant_ISYES:
          EXTEND(SP, 1);
          PUSHs(&PL_sv_undef);
          PUSHs(&PL_sv_yes);
          break; */
        default:
          sv = sv_2mortal(newSVpvf(
	    "Unexpected return type %d while processing PDL::IO::Image macro %s, used",
               type, s));
          PUSHs(sv);
        }