Format a double into a short string with units suffix

Double+Suffix.swift

extension Double {

    var suffixNumber: String {
        get {
            var num = self
            let sign = num < 0 ? "-" : ""

            num = fabs(num)
            if num < 1000.0 {
                return "\(sign)\(Int(num))"
            }

            let exp = Int(log10(num) / 3.0 )
            let units = ["K", "M", "G", "T", "P", "E"]
            let roundedNum = round(10 * num / pow(1000.0, Double(exp))) / 10
            return "\(sign)\(roundedNum)\(units[exp - 1])"
        }
    }

}