Excel PMT Formula in Swift

excel.pmt.formula.swift

class ExcelFormulas {
	class func pmt(rate : Double, nper : Double, pv : Double, fv : Double = 0, type : Double = 0) -> Double {
		return ((-pv * pvif(rate, nper: nper) - fv) / ((1.0 + rate * type) * fvifa(rate, nper: nper)))
	}
	
	class func pow1pm1(x : Double, y : Double) -> Double {
		return (x <= -1) ? pow((1 + x), y) - 1 : exp(y * log(1.0 + x)) - 1
	}
	
	class func pow1p(x : Double, y : Double) -> Double {
		return (abs(x) > 0.5) ? pow((1 + x), y) : exp(y * log(1.0 + x))
	}
	
	class func pvif(rate : Double, nper : Double) -> Double {
		return pow1p(rate, y: nper)
	}
	
	class func fvifa(rate : Double, nper : Double) -> Double {
		return (rate == 0) ? nper : pow1pm1(rate, y: nper) / rate
	}

}

Thanks for code!