PHPOffice / PhpSpreadsheet

            $fRet = -log($fNum2) * self::BESSELI($fNum, 0) +

                (-0.57721566 + $y * (0.42278420 + $y * (0.23069756 + $y * (0.3488590e-1 + $y * (0.262698e-2 + $y *

                                    (0.10750e-3 + $y * 0.74e-5))))));

        } else {

            $y = 2 / $fNum;

            $fRet = exp(-$fNum) / sqrt($fNum) *

                (1.25331414 + $y * (-0.7832358e-1 + $y * (0.2189568e-1 + $y * (-0.1062446e-1 + $y *

                                (0.587872e-2 + $y * (-0.251540e-2 + $y * 0.53208e-3))))));

        }

        return $fRet;

    }

            $fRet = log($fNum2) * self::BESSELI($fNum, 1) +

                (1 + $y * (0.15443144 + $y * (-0.67278579 + $y * (-0.18156897 + $y * (-0.1919402e-1 + $y *

                                    (-0.110404e-2 + $y * (-0.4686e-4))))))) / $fNum;

        } else {

            $y = 2 / $fNum;

            $fRet = exp(-$fNum) / sqrt($fNum) *

                (1.25331414 + $y * (0.23498619 + $y * (-0.3655620e-1 + $y * (0.1504268e-1 + $y * (-0.780353e-2 + $y *

                                    (0.325614e-2 + $y * (-0.68245e-3)))))));

        }

        return $fRet;

    }