Calculate CRC CCITT Swift 5

calculatecrt.swift

    /// Calcola il crc16 ( CRC-CCITT ) di un array di bytes nella rappresentazione UInt8
    ///
    /// - Parameters:
    ///     - input: Array di UInt8
    /// - Returns: valore in due bytes in formato UInt16
    public func getCRC(input : [UInt8]) -> UInt16 {
        if input.count == 0 { return 0 }
        var crc: UInt16 = 0xFFFF;          // initial value
        let polynomial: UInt16 = 0x1021;   // 0001 0000 0010 0001  (0, 5, 12)
        
        for b in input {
            var i = 0
            while (i < 8){
                let bit = ((b   >> (7-i) & 1) == 1) // boolean
                let c15 = ((crc >> 15    & 1) == 1) // boolean
                crc <<= 1
                if (XORCase(lhs: bit, rhs: c15)) { // equivale a bit ^ c15
                    crc ^= polynomial
                }
                i += 1
            }
            crc &= 0xffff
            
        }
        return crc
    }