/* sets formula for xylookup */
_xylform(s1, c1, s2, c2, s3, mode, intp, oor)
{
        local xystr, formstr;

        if (mode != 0)   /* x y */
        {
                xystr = sprintf("Xylookup(col(%s, %d), col(%s, %d), %s", s1, c1, s2, c2, s3);
        }
        else
        {
                xystr = sprintf("Xylookup(%s, %s", s1, s3);
        }
        if (intp == 0)
        {
                formstr = sprintf('%s, "none")', xystr);
        }
        else if (intp == 1)
        {
                if (oor == 0)
                {
                        formstr = sprintf("%s)", xystr);
                }
                else
                {
                        formstr = sprintf('%s, "linear", %d)', xystr, oor);
                }
        }
        else
        {
                if (oor == 0)
                {
                        formstr = sprintf('%s, "spline")', xystr);
                }
                else
                {
                        formstr = sprintf('%s, "spline", %d)', xystr, oor);
                }
        }
        return(formstr);
}