int callComp( SV* cmp, SV* a, SV* b ) {
	dSP;
	int rv;
	ENTER; 
	SAVETMPS; 
	
	PUSHMARK(SP);
	XPUSHs( newSViv( SvIVX( a ) ) );
	XPUSHs( newSViv( SvIVX( b ) ) );
	PUTBACK;

	if( call_sv( cmp, G_SCALAR ) != 1 )
		croak( "Bad comparator" );
	SPAGAIN;

	rv = POPi;

	PUTBACK; // << Was missing and is required!
	FREETMPS;LEAVE;
	return rv;
}