Arduino CRC32C 與 CRC32

Question

我正在嘗試為我的 Arduino 編寫一個函數，該函數接受一個十六進制char *並返回其十六進制校驗和。 我已經能夠解析和遍歷我的char *但我沒有得到正確的校驗和返回。 有人可以幫我找到我的錯誤或更好的計算方法嗎？

所以最初我嘗試按照本教程進行 CRC32 並將其修改為 CRC32C。 然后我看到了這段代碼並決定它對我來說更容易理解，這就是我當前代碼的基礎。

這是我當前的代碼：

static unsigned long crc_table[256] = {
  0x00000000, 0xf26b8303, 0xe13b70f7, 0x1350f3f4, 0xc79a971f, 0x35f1141c, 0x26a1e7e8, 0xd4ca64eb,
  0x8ad958cf, 0x78b2dbcc, 0x6be22838, 0x9989ab3b, 0x4d43cfd0, 0xbf284cd3, 0xac78bf27, 0x5e133c24,
  0x105ec76f, 0xe235446c, 0xf165b798, 0x030e349b, 0xd7c45070, 0x25afd373, 0x36ff2087, 0xc494a384,
  0x9a879fa0, 0x68ec1ca3, 0x7bbcef57, 0x89d76c54, 0x5d1d08bf, 0xaf768bbc, 0xbc267848, 0x4e4dfb4b,
  0x20bd8ede, 0xd2d60ddd, 0xc186fe29, 0x33ed7d2a, 0xe72719c1, 0x154c9ac2, 0x061c6936, 0xf477ea35,
  0xaa64d611, 0x580f5512, 0x4b5fa6e6, 0xb93425e5, 0x6dfe410e, 0x9f95c20d, 0x8cc531f9, 0x7eaeb2fa,
  0x30e349b1, 0xc288cab2, 0xd1d83946, 0x23b3ba45, 0xf779deae, 0x05125dad, 0x1642ae59, 0xe4292d5a,
  0xba3a117e, 0x4851927d, 0x5b016189, 0xa96ae28a, 0x7da08661, 0x8fcb0562, 0x9c9bf696, 0x6ef07595,
  0x417b1dbc, 0xb3109ebf, 0xa0406d4b, 0x522bee48, 0x86e18aa3, 0x748a09a0, 0x67dafa54, 0x95b17957,
  0xcba24573, 0x39c9c670, 0x2a993584, 0xd8f2b687, 0x0c38d26c, 0xfe53516f, 0xed03a29b, 0x1f682198,
  0x5125dad3, 0xa34e59d0, 0xb01eaa24, 0x42752927, 0x96bf4dcc, 0x64d4cecf, 0x77843d3b, 0x85efbe38,
  0xdbfc821c, 0x2997011f, 0x3ac7f2eb, 0xc8ac71e8, 0x1c661503, 0xee0d9600, 0xfd5d65f4, 0x0f36e6f7, 
  0x61c69362, 0x93ad1061, 0x80fde395, 0x72966096, 0xa65c047d, 0x5437877e, 0x4767748a, 0xb50cf789, 
  0xeb1fcbad, 0x197448ae, 0x0a24bb5a, 0xf84f3859, 0x2c855cb2, 0xdeeedfb1, 0xcdbe2c45, 0x3fd5af46, 
  0x7198540d, 0x83f3d70e, 0x90a324fa, 0x62c8a7f9, 0xb602c312, 0x44694011, 0x5739b3e5, 0xa55230e6, 
  0xfb410cc2, 0x092a8fc1, 0x1a7a7c35, 0xe811ff36, 0x3cdb9bdd, 0xceb018de, 0xdde0eb2a, 0x2f8b6829, 
  0x82f63b78, 0x709db87b, 0x63cd4b8f, 0x91a6c88c, 0x456cac67, 0xb7072f64, 0xa457dc90, 0x563c5f93, 
  0x082f63b7, 0xfa44e0b4, 0xe9141340, 0x1b7f9043, 0xcfb5f4a8, 0x3dde77ab, 0x2e8e845f, 0xdce5075c, 
  0x92a8fc17, 0x60c37f14, 0x73938ce0, 0x81f80fe3, 0x55326b08, 0xa759e80b, 0xb4091bff, 0x466298fc, 
  0x1871a4d8, 0xea1a27db, 0xf94ad42f, 0x0b21572c, 0xdfeb33c7, 0x2d80b0c4, 0x3ed04330, 0xccbbc033, 
  0xa24bb5a6, 0x502036a5, 0x4370c551, 0xb11b4652, 0x65d122b9, 0x97baa1ba, 0x84ea524e, 0x7681d14d, 
  0x2892ed69, 0xdaf96e6a, 0xc9a99d9e, 0x3bc21e9d, 0xef087a76, 0x1d63f975, 0x0e330a81, 0xfc588982, 
  0xb21572c9, 0x407ef1ca, 0x532e023e, 0xa145813d, 0x758fe5d6, 0x87e466d5, 0x94b49521, 0x66df1622, 
  0x38cc2a06, 0xcaa7a905, 0xd9f75af1, 0x2b9cd9f2, 0xff56bd19, 0x0d3d3e1a, 0x1e6dcdee, 0xec064eed, 
  0xc38d26c4, 0x31e6a5c7, 0x22b65633, 0xd0ddd530, 0x0417b1db, 0xf67c32d8, 0xe52cc12c, 0x1747422f, 
  0x49547e0b, 0xbb3ffd08, 0xa86f0efc, 0x5a048dff, 0x8ecee914, 0x7ca56a17, 0x6ff599e3, 0x9d9e1ae0,
  0xd3d3e1ab, 0x21b862a8, 0x32e8915c, 0xc083125f, 0x144976b4, 0xe622f5b7, 0xf5720643, 0x07198540, 
  0x590ab964, 0xab613a67, 0xb831c993, 0x4a5a4a90, 0x9e902e7b, 0x6cfbad78, 0x7fab5e8c, 0x8dc0dd8f, 
  0xe330a81a, 0x115b2b19, 0x020bd8ed, 0xf0605bee, 0x24aa3f05, 0xd6c1bc06, 0xc5914ff2, 0x37faccf1, 
  0x69e9f0d5, 0x9b8273d6, 0x88d28022, 0x7ab90321, 0xae7367ca, 0x5c18e4c9, 0x4f48173d, 0xbd23943e, 
  0xf36e6f75, 0x0105ec76, 0x12551f82, 0xe03e9c81, 0x34f4f86a, 0xc69f7b69, 0xd5cf889d, 0x27a40b9e, 
  0x79b737ba, 0x8bdcb4b9, 0x988c474d, 0x6ae7c44e, 0xbe2da0a5, 0x4c4623a6, 0x5f16d052, 0xad7d5351 
};

unsigned long crc_string(char *s)
{
  unsigned long crc = 0xffffffff; 
  while (*s){
    crc = crc_table[(crc ^ ((uint8_t) hex2int(*s++))) & 0xff] ^ (crc >> 8);
  }
  crc = ~crc;
  
  return crc;
}

int hex2int(char ch)
{
    if (ch >= '0' && ch <= '9')
        return ch - '0';
    if (ch >= 'A' && ch <= 'F')
        return ch - 'A' + 10;
    if (ch >= 'a' && ch <= 'f')
        return ch - 'a' + 10;
    return -1;
}

我正在使用的數據包示例是：

B100880000000000C840C000160C0E0E2400CD19921979194B00004B00004A00004B00004B00004A00004A00004B00004B00004B00004A00004A00004B00004A00004A00004B00004A00004B00004A00004B00004B00004B00004A00004A00004A00004B00004A00004B00004A00004A00004B00004B00004A00004B00004B00004A00004B00004B0D66BC1B0D0A

其中校驗和為： 0D66BC1B

我函數的校驗和是： 348BA995

進入crc_string的數據為：

00000000C840C000160C0E0E2400CD19921979194B00004B00004A00004B00004B00004A00004A00004B00004B00004B00004A00004A00004B00004A00004A00004B00004A00004B00004A00004B00004B00004B00004A00004A00004A00004B00004A00004B00004A00004A00004B00004B00004A00004B00004B00004A00004B00004B

其他信息：
數據最初是在一個字節數組中接收的，為了便於閱讀，該數組已更改為十六進制字符串。 詳情請看以下函數：

void array_to_string(byte array[], unsigned int len, char buffer[]) {
  for (unsigned int i = 0; i < len; i++) {  // make this len*2 ? to avoid buffer overflow
    byte nib1 = (array[i] >> 4) & 0x0F;
    byte nib2 = (array[i] >> 0) & 0x0F;
    buffer[i * 2 + 0] = nib1 < 0xA ? '0' + nib1 : 'A' + nib1 - 0xA;
    buffer[i * 2 + 1] = nib2 < 0xA ? '0' + nib2 : 'A' + nib2 - 0xA;
  }
  buffer[len * 2] = '\0';
}

以下是我正在處理的文件的較大部分。 currentDataString 的示例等同於上面列出的“數據包示例”。

void array_to_string(byte array[], unsigned int len, char buffer[]) {
  for (unsigned int i = 0; i < len; i++) {  // make this len*2 ? to avoid buffer overflow
    byte nib1 = (array[i] >> 4) & 0x0F;
    byte nib2 = (array[i] >> 0) & 0x0F;
    buffer[i * 2 + 0] = nib1 < 0xA ? '0' + nib1 : 'A' + nib1 - 0xA;
    buffer[i * 2 + 1] = nib2 < 0xA ? '0' + nib2 : 'A' + nib2 - 0xA;
  }
  buffer[len * 2] = '\0';
}

static void notifyCallback(BLERemoteCharacteristic *pBLERemoteCharacteristic, byte pData[], size_t length, bool isNotify) {
  array_to_string(pData, length, currentData);
  Serial.print(F("Clean data: "));
  Serial.println(currentData);
  String currentDataString(currentData);
  else if(currentDataString.indexOf("B100")!= -1){ 
    Serial.println("b100 Data");
    if(checkCRC(currentDataString)){
      Serial.println("Good Data");
    }
  }
}

boolean checkCRC(String currentDataString){
  int len = currentDataString.length(); 
  String newCRC = currentDataString.substring(8,len - 12 );
  char buf[len- 8 - 12];
  newCRC.toCharArray(buf, len-8-12);
  unsigned long newFunction = crc_string(buf);
  Serial.println(crc_string(buf), HEX);
  Serial.print(F("newCRC: "));
  Serial.println(newCRC);

  String GivenCRC = currentDataString.substring(len - 4 - 8 ,len - 4 ); 
  Serial.print(F("GivenCRC: "));
  Serial.println(GivenCRC);
  return newCRC == GivenCRC;
}

Answer 1

如果您要發送原始字節，這應該可以正常工作：

編輯：抱歉，原來的解決方案只關注生成crc的內容。 我也添加了一個len參數。

unsigned long crc_string(char *s, int len)
{
  unsigned long crc = 0xffffffff; 
  int i = 0;
  for (; i < len; ++i){
    crc = crc_table[((crc << 8) ^ *s++) & 0xff] ^ (crc >> 8);
  }
  crc = ~crc;
  
  return crc;
}

另一種方法是發送一個seed參數，這樣您就可以更好地實時進行 crc。

unsigned long crc_string(char *s, int len, unsigned long seed)

然后，您首先將crc設置為seed而不是0xffffffff 。

如果你有這樣的東西，你所擁有的將會起作用：

const char* s = "ab0c135a";
crc_string(s);

如果您真的得到十六進制字符串，我會感到非常驚訝。

Answer 2

最好的解決方案是在將字節數組轉換為十六進制字符串之前計算 CRC。 在問題中添加一個最小的可重現示例以獲得詳細的解決方案。

如果十六進制字符串表示僅用於調試/打印，則可能有不需要轉換整個字節數組的替代方案。

---

您的 CRC 表專為 8 位輸入值而設計，而您的函數hex2int轉換僅代表 4 位的單個字符。

這意味着您將錯誤的數據輸入到 CRC 計算中。

這可以通過將十六進制字符串輸入的兩個字符轉換為輸入 CRC 計算的字節來解決。

int hex2nibble(char ch)
{
    if (ch >= '0' && ch <= '9')
        return ch - '0';
    if (ch >= 'A' && ch <= 'F')
        return ch - 'A' + 10;
    if (ch >= 'a' && ch <= 'f')
        return ch - 'a' + 10;
    return -1;
}

int hex2byte(const char *p)
{
    int byte = hex2nibble(*p++);
    /* If the 1st character was invalid we want to keep the -1. */
    if(byte >= 0)
    {
        /* Cast to unsigned because bit operations on signed data might be implementation defined. */
        unsigned int val = (unsigned int)byte;
        val <<= 4;
        val |= (unsigned int)hex2nibble(*p);
        byte = (int)val;
    }
    return byte;
}

/* I suggest to replace unsigned int with uint32_t for portable code.*/
unsigned int crc_string(const char *s)
{
    unsigned int crc = 0xffffffff; 
    while (*s){
        /* note: missing error handling for return value -1 */
        crc = crc_table[(crc ^ ((uint8_t) hex2byte(s))) & 0xff] ^ (crc >> 8);
        s += 2;
    }
    crc = ~crc;
  
    return crc;
}

我無法在 Arduino 上測試建議的代碼。

---

代碼的測試標准 C++ 版本：

#include <iostream>
#include <cstdint>

using namespace std;

static uint32_t crc_table[256] = {
  0x00000000, 0xf26b8303, 0xe13b70f7, 0x1350f3f4, 0xc79a971f, 0x35f1141c, 0x26a1e7e8, 0xd4ca64eb,
  0x8ad958cf, 0x78b2dbcc, 0x6be22838, 0x9989ab3b, 0x4d43cfd0, 0xbf284cd3, 0xac78bf27, 0x5e133c24,
  0x105ec76f, 0xe235446c, 0xf165b798, 0x030e349b, 0xd7c45070, 0x25afd373, 0x36ff2087, 0xc494a384,
  0x9a879fa0, 0x68ec1ca3, 0x7bbcef57, 0x89d76c54, 0x5d1d08bf, 0xaf768bbc, 0xbc267848, 0x4e4dfb4b,
  0x20bd8ede, 0xd2d60ddd, 0xc186fe29, 0x33ed7d2a, 0xe72719c1, 0x154c9ac2, 0x061c6936, 0xf477ea35,
  0xaa64d611, 0x580f5512, 0x4b5fa6e6, 0xb93425e5, 0x6dfe410e, 0x9f95c20d, 0x8cc531f9, 0x7eaeb2fa,
  0x30e349b1, 0xc288cab2, 0xd1d83946, 0x23b3ba45, 0xf779deae, 0x05125dad, 0x1642ae59, 0xe4292d5a,
  0xba3a117e, 0x4851927d, 0x5b016189, 0xa96ae28a, 0x7da08661, 0x8fcb0562, 0x9c9bf696, 0x6ef07595,
  0x417b1dbc, 0xb3109ebf, 0xa0406d4b, 0x522bee48, 0x86e18aa3, 0x748a09a0, 0x67dafa54, 0x95b17957,
  0xcba24573, 0x39c9c670, 0x2a993584, 0xd8f2b687, 0x0c38d26c, 0xfe53516f, 0xed03a29b, 0x1f682198,
  0x5125dad3, 0xa34e59d0, 0xb01eaa24, 0x42752927, 0x96bf4dcc, 0x64d4cecf, 0x77843d3b, 0x85efbe38,
  0xdbfc821c, 0x2997011f, 0x3ac7f2eb, 0xc8ac71e8, 0x1c661503, 0xee0d9600, 0xfd5d65f4, 0x0f36e6f7, 
  0x61c69362, 0x93ad1061, 0x80fde395, 0x72966096, 0xa65c047d, 0x5437877e, 0x4767748a, 0xb50cf789, 
  0xeb1fcbad, 0x197448ae, 0x0a24bb5a, 0xf84f3859, 0x2c855cb2, 0xdeeedfb1, 0xcdbe2c45, 0x3fd5af46, 
  0x7198540d, 0x83f3d70e, 0x90a324fa, 0x62c8a7f9, 0xb602c312, 0x44694011, 0x5739b3e5, 0xa55230e6, 
  0xfb410cc2, 0x092a8fc1, 0x1a7a7c35, 0xe811ff36, 0x3cdb9bdd, 0xceb018de, 0xdde0eb2a, 0x2f8b6829, 
  0x82f63b78, 0x709db87b, 0x63cd4b8f, 0x91a6c88c, 0x456cac67, 0xb7072f64, 0xa457dc90, 0x563c5f93, 
  0x082f63b7, 0xfa44e0b4, 0xe9141340, 0x1b7f9043, 0xcfb5f4a8, 0x3dde77ab, 0x2e8e845f, 0xdce5075c, 
  0x92a8fc17, 0x60c37f14, 0x73938ce0, 0x81f80fe3, 0x55326b08, 0xa759e80b, 0xb4091bff, 0x466298fc, 
  0x1871a4d8, 0xea1a27db, 0xf94ad42f, 0x0b21572c, 0xdfeb33c7, 0x2d80b0c4, 0x3ed04330, 0xccbbc033, 
  0xa24bb5a6, 0x502036a5, 0x4370c551, 0xb11b4652, 0x65d122b9, 0x97baa1ba, 0x84ea524e, 0x7681d14d, 
  0x2892ed69, 0xdaf96e6a, 0xc9a99d9e, 0x3bc21e9d, 0xef087a76, 0x1d63f975, 0x0e330a81, 0xfc588982, 
  0xb21572c9, 0x407ef1ca, 0x532e023e, 0xa145813d, 0x758fe5d6, 0x87e466d5, 0x94b49521, 0x66df1622, 
  0x38cc2a06, 0xcaa7a905, 0xd9f75af1, 0x2b9cd9f2, 0xff56bd19, 0x0d3d3e1a, 0x1e6dcdee, 0xec064eed, 
  0xc38d26c4, 0x31e6a5c7, 0x22b65633, 0xd0ddd530, 0x0417b1db, 0xf67c32d8, 0xe52cc12c, 0x1747422f, 
  0x49547e0b, 0xbb3ffd08, 0xa86f0efc, 0x5a048dff, 0x8ecee914, 0x7ca56a17, 0x6ff599e3, 0x9d9e1ae0,
  0xd3d3e1ab, 0x21b862a8, 0x32e8915c, 0xc083125f, 0x144976b4, 0xe622f5b7, 0xf5720643, 0x07198540, 
  0x590ab964, 0xab613a67, 0xb831c993, 0x4a5a4a90, 0x9e902e7b, 0x6cfbad78, 0x7fab5e8c, 0x8dc0dd8f, 
  0xe330a81a, 0x115b2b19, 0x020bd8ed, 0xf0605bee, 0x24aa3f05, 0xd6c1bc06, 0xc5914ff2, 0x37faccf1, 
  0x69e9f0d5, 0x9b8273d6, 0x88d28022, 0x7ab90321, 0xae7367ca, 0x5c18e4c9, 0x4f48173d, 0xbd23943e, 
  0xf36e6f75, 0x0105ec76, 0x12551f82, 0xe03e9c81, 0x34f4f86a, 0xc69f7b69, 0xd5cf889d, 0x27a40b9e, 
  0x79b737ba, 0x8bdcb4b9, 0x988c474d, 0x6ae7c44e, 0xbe2da0a5, 0x4c4623a6, 0x5f16d052, 0xad7d5351 
};

int hex2nibble(char ch)
{
    if (ch >= '0' && ch <= '9')
        return ch - '0';
    if (ch >= 'A' && ch <= 'F')
        return ch - 'A' + 10;
    if (ch >= 'a' && ch <= 'f')
        return ch - 'a' + 10;
    return -1;
}

int hex2byte(const char *p)
{
    int byte = hex2nibble(*p++);
    /* If the 1st character was invalid we want to keep the -1. */
    if(byte >= 0)
    {
        /* Cast to unsigned because bit operations on signed data might be implementation defined. */
        unsigned int val = (unsigned int)byte;
        val <<= 4;
        val |= (unsigned int)hex2nibble(*p);
        byte = (int)val;
    }
    return byte;
}

/* Replaced unsigned int with uint32_t for portable code. */
uint32_t crc_string(const char *s)
{
    uint32_t crc = 0xffffffff; 
    while (*s){
        /* note: missing error handling for return value -1 */
        crc = crc_table[(crc ^ ((uint8_t) hex2byte(s))) & 0xff] ^ (crc >> 8);
        s += 2;
    }
    crc = ~crc;
  
    return crc;
}

int main()
{
    string currentDataString = "B100880000000000C840C000160C0E101E00B219761954194C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004D00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004D00004C00004CDC49F5C30D0A";

    cout << "input:      " << currentDataString << endl;
  
    int len = currentDataString.length();
    string newCRC = currentDataString.substr(8, len - 12 -8 );
  
    const char *buf = newCRC.c_str();
  
    cout << "newCRCFrom: " << "        " << newCRC << endl;
    cout << "newCRC:     " << hex << crc_string(buf) << endl;
  
    string GivenCRC = currentDataString.substr(len - 4 - 8, 8); // TODO we only need to put the CRC to a string not the whole packet
    cout << "GivenCRC:   " << GivenCRC << endl;

    cout << "Valid:      " << (newCRC == GivenCRC) << endl;
    
    return 0;
}

輸出：

input:      B100880000000000C840C000160C0E101E00B219761954194C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004D00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004D00004C00004CDC49F5C30D0A
newCRCFrom:         00000000C840C000160C0E101E00B219761954194C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004D00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004C00004D00004C00004C
newCRC:     c3f549dc
GivenCRC:   DC49F5C3
Valid:      0

如您所見，計算出的 CRC 基本相同，但數據字符串包含 CRC 作為小端字節順序的字節，而計算出的 CRC 字符串顯示正常字節順序的 4 字節數字的十六進制表示.

問題中缺少 CRC 以小端字節順序存儲的信息。 （這應該是我在評論中要求的規范的一部分。）

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鏈接的Arduino 示例中的表用於 4 位輸入， crc_update將 8 位輸入拆分為兩個 4 位值。 如果您想將 4 位值輸入 CRC 計算，則可以使用此表。 Arduino 解決方案首先將低半字節送入 CRC 計算。 下面未經測試的提議將首先提供較高的半字節，因此此計算可能是錯誤的。

static PROGMEM prog_uint32_t crc_table[16] = {
    0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac,
    0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c,
    0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c,
    0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c
};

unsigned long crc_string(char *s)
{
    unsigned long crc = 0xffffffff; 
    while (*s){
        crc = pgm_read_dword_near(crc_table + ((uint8_t) hex2int(*s++) & 0x0f))
            ^ (crc >> 4);
    }
    crc = ~crc;
  
    return crc;
}