Kotlin 用浮点数或十进制数给出错误答案的阶乘计算

这段代码可以很好地计算阶乘，但是用浮点数或十进制数给出错误的答案

    fun factorial(number: BigDecimal): BigDecimal {
        if (number >= BigDecimal(3000)) {
            is_infinity = true
            return BigDecimal.ZERO
        }
        return if (number < BigDecimal.ZERO) {
            domain_error = true
            BigDecimal.ZERO
        } else {
            val decimalPartOfNumber = number.toDouble() - number.toInt()
            if (decimalPartOfNumber == 0.0) {
                var factorial = BigInteger("1")
                for (i in 1..number.toInt()) {
                    factorial *= i.toBigInteger()
                }
                factorial.toBigDecimal()
            } else gammaLanczos(number + BigDecimal.ONE)
        }
    }

    private fun gammaLanczos(x: BigDecimal): BigDecimal {
        // https://rosettacode.org/wiki/Gamma_function
        var xx = x
        val p = doubleArrayOf(
            0.9999999999998099,
            676.5203681218851,
            -1259.1392167224028,
            771.3234287776531,
            -176.6150291621406,
            12.507343278686905,
            -0.13857109526572012,
            9.984369578019572E-6,
            1.5056327351493116e-7
        )
        val g = BigDecimal(7)
        if (xx < BigDecimal(0.5)) return (Math.PI / (sin(Math.PI * xx.toDouble()) * gammaLanczos(BigDecimal(1.0 - xx.toDouble())).toDouble())).toBigDecimal()
        xx--
        var a = p[0]
        val t = xx + g + BigDecimal(0.5)
        for (i in 1 until p.size) a += p[i] / (xx.toDouble() + i)
        return (sqrt(2.0 * Math.PI) * t.toDouble().pow(xx.toInt() + 0.5) * exp(-t.toDouble()) * a).toBigDecimal()
    }

对于下面的代码，测试在运行9个代码后失败，

@Test
    fun sqrt() {

        val result =  NumberFormatter.factorial(BigDecimal(3.03))
        assertEquals(6.23120891259, result.toFloat())
    }

得到这个预期:6.23120891259但是:5.8062997<><>

有人能帮我吗.谢谢