swift - CCITT 在 Swift 中实现

Question

我如何快速实现 CRC-CCITT。我设法让它在 Java 上运行

public static String createCRC(String string) {

    String crcCode = "";

    int crc = 0xFFFF;          // initial value
    int polynomial = 0x1021;   // 0001 0000 0010 0001  (0, 5, 12)

    // byte[] testBytes = "123456789".getBytes("ASCII");

    byte[] bytes = string.getBytes();

    for (byte b : bytes) {
        for (int i = 0; i < 8; i++) {
            boolean bit = ((b   >> (7-i) & 1) == 1);
            boolean c15 = ((crc >> 15    & 1) == 1);
            crc <<= 1;
            if (c15 ^ bit) crc ^= polynomial;
        }
    }

    crc &= 0xffff;
    crcCode = Integer.toHexString(crc).toUpperCase();

    return crcCode;

}

谁能帮我转换成 Swift。或者我可以使用与此功能类似的其他文件？

谢谢

Answer 1

使用经典的“表格”方法

let crc_table: [UInt16] = [
    
    0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
    0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef,
    0x1231, 0x0210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
    0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de,
    0x2462, 0x3443, 0x0420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485,
    0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
    0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6, 0x5695, 0x46b4,
    0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc,
    0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
    0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b,
    0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12,
    0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
    0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41,
    0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49,
    0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70,
    0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78,
    0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f,
    0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
    0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e,
    0x02b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256,
    0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
    0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
    0xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c,
    0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
    0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab,
    0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882, 0x28a3,
    0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
    0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92,
    0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9,
    0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1,
    0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8,
    0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0
]


func crc16Ccitt(data: [UInt8], seed: UInt16, final: UInt16)->UInt16
{
    
    var crc: UInt32 = UInt32(seed)
    var temp: UInt32 = 0
    
    data.forEach { byte in
        temp = UInt32(byte) ^ (crc >> 8) & 0xff
        crc = UInt32(crc_table[Int(temp)]) ^ (crc << 8)
    }
    
    return UInt16((crc ^ UInt32(final)) & 0xffff)
}

// test it first

print(crc16Ccitt(data: "".utf8.map{$0}, seed: 0x1D0F, final: 0) == 0x1d0f)
print(crc16Ccitt(data: "A".utf8.map{$0}, seed: 0x1D0F, final: 0) == 0x9479)
print(crc16Ccitt(data: "123456789".utf8.map{$0}, seed: 0x1D0F, final: 0) == 0xe5cc)

打印

true
true
true

或者这个非常简短的 Swift 版本

func crc16ccitt(data: [UInt8],seed: UInt16 = 0x1d0f, final: UInt16 = 0xffff)->UInt16{
    var crc = seed
    data.forEach { (byte) in
        crc ^= UInt16(byte) << 8
        (0..<8).forEach({ _ in
            crc = (crc & 0x8000) != 0 ? (crc << 1) ^ 0x1021 : crc << 1
        })
    }
    return crc & final
}
print(crc16ccitt(data: "".utf8.map{$0}) == 0x1d0f)
print(crc16ccitt(data: "A".utf8.map{$0}) == 0x9479)
print(crc16ccitt(data: "123456789".utf8.map{$0}) == 0xe5cc)

打印

true
true
true