如何从 16 位数据计算 CRC-32？

Question

How would I (in C/C++) calculate the CRC32 from the following 16-bit data?

The data is:

0x0000, 0x083A, 0x0000, 0xFFF7, 0x0000, 0xFFFE, 0x0000, 0x0001, 0x5001, 0x0003, 0xE00A, 0x0015, 0xC009, 0x0320, 0x8A54

I assume the CRC32 = 0xB6C815B4 according to the following (from the ADIS16495 datasheet):

I managed to get the correct CRC32 online ( Link to online CRC page ).

I swapped the byte order of the 8-bit pairs.

But I don't know how to implement it in C. There is at least a pre-calculated lookup table on the page.

Answer 1

I managed to get the correct CRC32 online ( Link to online CRC page ).

I swapped the byte order of the 8-bit pairs.

Screen dump of CRC32 calculation

And also managed to solve the C implementation (don't know if this is the optimal solution):

#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>

uint16_t data[15] = {
    0x0000, 0x083A, 0x0000, 0xFFF7, 0x0000, 0xFFFE, 0x0000, 0x0001, 0x5001, 0x0003, 0xE00A, 0x0015, 0xC009, 0x0320, 0x8A54
};

const uint32_t crcTable[] = {
0x00000000, 0x04C11DB7, 0x09823B6E, 0x0D4326D9, 0x130476DC, 0x17C56B6B, 0x1A864DB2, 0x1E475005, 
0x2608EDB8, 0x22C9F00F, 0x2F8AD6D6, 0x2B4BCB61, 0x350C9B64, 0x31CD86D3, 0x3C8EA00A, 0x384FBDBD, 
0x4C11DB70, 0x48D0C6C7, 0x4593E01E, 0x4152FDA9, 0x5F15ADAC, 0x5BD4B01B, 0x569796C2, 0x52568B75, 
0x6A1936C8, 0x6ED82B7F, 0x639B0DA6, 0x675A1011, 0x791D4014, 0x7DDC5DA3, 0x709F7B7A, 0x745E66CD, 
0x9823B6E0, 0x9CE2AB57, 0x91A18D8E, 0x95609039, 0x8B27C03C, 0x8FE6DD8B, 0x82A5FB52, 0x8664E6E5, 
0xBE2B5B58, 0xBAEA46EF, 0xB7A96036, 0xB3687D81, 0xAD2F2D84, 0xA9EE3033, 0xA4AD16EA, 0xA06C0B5D, 
0xD4326D90, 0xD0F37027, 0xDDB056FE, 0xD9714B49, 0xC7361B4C, 0xC3F706FB, 0xCEB42022, 0xCA753D95, 
0xF23A8028, 0xF6FB9D9F, 0xFBB8BB46, 0xFF79A6F1, 0xE13EF6F4, 0xE5FFEB43, 0xE8BCCD9A, 0xEC7DD02D, 
0x34867077, 0x30476DC0, 0x3D044B19, 0x39C556AE, 0x278206AB, 0x23431B1C, 0x2E003DC5, 0x2AC12072, 
0x128E9DCF, 0x164F8078, 0x1B0CA6A1, 0x1FCDBB16, 0x018AEB13, 0x054BF6A4, 0x0808D07D, 0x0CC9CDCA, 
0x7897AB07, 0x7C56B6B0, 0x71159069, 0x75D48DDE, 0x6B93DDDB, 0x6F52C06C, 0x6211E6B5, 0x66D0FB02, 
0x5E9F46BF, 0x5A5E5B08, 0x571D7DD1, 0x53DC6066, 0x4D9B3063, 0x495A2DD4, 0x44190B0D, 0x40D816BA, 
0xACA5C697, 0xA864DB20, 0xA527FDF9, 0xA1E6E04E, 0xBFA1B04B, 0xBB60ADFC, 0xB6238B25, 0xB2E29692, 
0x8AAD2B2F, 0x8E6C3698, 0x832F1041, 0x87EE0DF6, 0x99A95DF3, 0x9D684044, 0x902B669D, 0x94EA7B2A, 
0xE0B41DE7, 0xE4750050, 0xE9362689, 0xEDF73B3E, 0xF3B06B3B, 0xF771768C, 0xFA325055, 0xFEF34DE2, 
0xC6BCF05F, 0xC27DEDE8, 0xCF3ECB31, 0xCBFFD686, 0xD5B88683, 0xD1799B34, 0xDC3ABDED, 0xD8FBA05A, 
0x690CE0EE, 0x6DCDFD59, 0x608EDB80, 0x644FC637, 0x7A089632, 0x7EC98B85, 0x738AAD5C, 0x774BB0EB, 
0x4F040D56, 0x4BC510E1, 0x46863638, 0x42472B8F, 0x5C007B8A, 0x58C1663D, 0x558240E4, 0x51435D53, 
0x251D3B9E, 0x21DC2629, 0x2C9F00F0, 0x285E1D47, 0x36194D42, 0x32D850F5, 0x3F9B762C, 0x3B5A6B9B, 
0x0315D626, 0x07D4CB91, 0x0A97ED48, 0x0E56F0FF, 0x1011A0FA, 0x14D0BD4D, 0x19939B94, 0x1D528623, 
0xF12F560E, 0xF5EE4BB9, 0xF8AD6D60, 0xFC6C70D7, 0xE22B20D2, 0xE6EA3D65, 0xEBA91BBC, 0xEF68060B, 
0xD727BBB6, 0xD3E6A601, 0xDEA580D8, 0xDA649D6F, 0xC423CD6A, 0xC0E2D0DD, 0xCDA1F604, 0xC960EBB3, 
0xBD3E8D7E, 0xB9FF90C9, 0xB4BCB610, 0xB07DABA7, 0xAE3AFBA2, 0xAAFBE615, 0xA7B8C0CC, 0xA379DD7B, 
0x9B3660C6, 0x9FF77D71, 0x92B45BA8, 0x9675461F, 0x8832161A, 0x8CF30BAD, 0x81B02D74, 0x857130C3, 
0x5D8A9099, 0x594B8D2E, 0x5408ABF7, 0x50C9B640, 0x4E8EE645, 0x4A4FFBF2, 0x470CDD2B, 0x43CDC09C, 
0x7B827D21, 0x7F436096, 0x7200464F, 0x76C15BF8, 0x68860BFD, 0x6C47164A, 0x61043093, 0x65C52D24, 
0x119B4BE9, 0x155A565E, 0x18197087, 0x1CD86D30, 0x029F3D35, 0x065E2082, 0x0B1D065B, 0x0FDC1BEC, 
0x3793A651, 0x3352BBE6, 0x3E119D3F, 0x3AD08088, 0x2497D08D, 0x2056CD3A, 0x2D15EBE3, 0x29D4F654, 
0xC5A92679, 0xC1683BCE, 0xCC2B1D17, 0xC8EA00A0, 0xD6AD50A5, 0xD26C4D12, 0xDF2F6BCB, 0xDBEE767C, 
0xE3A1CBC1, 0xE760D676, 0xEA23F0AF, 0xEEE2ED18, 0xF0A5BD1D, 0xF464A0AA, 0xF9278673, 0xFDE69BC4, 
0x89B8FD09, 0x8D79E0BE, 0x803AC667, 0x84FBDBD0, 0x9ABC8BD5, 0x9E7D9662, 0x933EB0BB, 0x97FFAD0C, 
0xAFB010B1, 0xAB710D06, 0xA6322BDF, 0xA2F33668, 0xBCB4666D, 0xB8757BDA, 0xB5365D03, 0xB1F740B4 
};

uint8_t reflect8(uint8_t b) {
    uint8_t from = 0x01;
    uint8_t to = 0x80;
    uint8_t r = 0;
    while(to)
    {
        if(b & from) r |= to;
        from <<= 1;
        to >>= 1;
    }
    return r;
}

uint32_t reflect32(uint32_t b) {
    uint32_t from = 0x00000001;
    uint32_t to = 0x80000000;
    uint32_t r = 0;
    while(to)
    {
        if(b & from) r |= to;
        from <<= 1;
        to >>= 1;
    }
    return r;
}

uint32_t
crc32 (const uint16_t *buf, size_t size)
{
  uint32_t crc;

  crc = 0xFFFFFFFF; /* CRC is set to specified initial value */
  while (size--)
  {
    /* Take LSB */

    uint8_t b = reflect8(*buf); /* Reflect input byte */

    /* XOR-in next input byte into MSB of crc and get this MSB, that's our new intermediate divident */
    uint8_t pos = (uint8_t)((crc ^ (b << 24)) >> 24);

    /* Shift out the MSB used for division per lookuptable and XOR with the remainder */
    crc = (crc << 8) ^ crcTable[pos];

    /* Take MSB */

    b = reflect8(*buf >> 8); /* Reflect input byte */
    buf++;

    /* XOR-in next input byte into MSB of crc and get this MSB, that's our new intermediate divident */
    pos = (uint8_t)((crc ^ (b << 24)) >> 24);

    /* Shift out the MSB used for division per lookuptable and XOR with the remainder */
    crc = (crc << 8) ^ crcTable[pos];
  }
  /* Reflect result crc */
  crc = reflect32(crc);
  /* Xor the crc value with specified final XOR value before returning */
  return crc ^ 0xFFFFFFFF;
}


int
main ()
{
  uint32_t crc = crc32(data, 15);
  printf("CRC = 0x%" PRIx32 "\n", crc);
  return 0;
}

Answer 2

Firstly the actual CRC-32 calculation has been dome many times, and made freely available from many sources. Here for example are several implementations to choose from, all share the same interface of the form:

unsigned int crc32(unsigned char *message);

This is not immediately suited to your needs as it assumes that message is a null-terminated text string rather than binary data, it also assumes a 32-bit int . So you need to remove those assumptions and explicitly pass the length. To avoid casting, you could make the data a void* :

uint32_t crc32( void* data, size_t length ) ;

Since you entered each value in low-byte/high-byte order in your test, then for a little-endian platform (such as an x86 PC or most ARM devices), then you do not need to swap the byte order

uint32_t crc = crc32( adis16495_data, sizeof(adis16495_data) ) ;

So adapting the second example at the link above (because it is the shortest, not because it is necessarily the best - in this case I doubt it matters), and cleaning up the code a little:

uint32_t crc32( void* data, size_t length ) 
{
   uint32_t byte ;
   uint32_t mask ;
   uint32_t crc = 0xFFFFFFFFu;
   uint8_t* byte_data = (uint8_t*)data ;

   for( int i = 0; i < length; i++) 
   {
      byte = byte_data[i];            // Get next byte.
      crc = crc ^ byte;
      for( int j = 7; j >= 0; j--) 
      {
         mask = -(crc & 1);
         crc = (crc >> 1) ^ (0xEDB88320u & mask);
      }
   }

   return ~crc;
} 

If you your data was in big-endian form, then rather than laboriously swapping the byte order, the the function could be specialised, explicitly for 16 bit data:

uint32_t crc32_16bit( uint16_t* data, size_t count ) 
{
   uint32_t byte ;
   uint32_t mask ;
   uint32_t crc = 0xFFFFFFFFu;
   size_t length = count * 2 ;

   for( int i = 0; i < length; i++) 
   {
      // Get next byte, LSB on even i, MSB on odd i
      byte = (i & 1) == 0) ? data[i] & 0x00FF : 
                             data[i] >> 8 ; 
      crc = crc ^ byte ;
      for( int j = 7; j >= 0; j--) 
      {
         mask = -(crc & 1);
         crc = (crc >> 1) ^ (0xEDB88320u & mask);
      }
   }

   return ~crc;
} 

In this, the count argument is the number of 16 bit words, not the byte length as before, so it might be called:

uint32_t crc = crc32( adis16495_data, sizeof(adis16495_data) / sizeof(uint16_t) ) ;

for example.