CRC

description

provides functions to calculate a crc (1-64bit)

note

Description for python implementation needs to be added

language

C, Python

usage

To calculate a CRC you need to have an initialized CRC handle (CRChandle_t). The handle can be initialized statically (see example 2). How to create the code please refer to example 3. Static initialization will save the time of calculating the CRC table which may take at least 3900 calculations which may important to your application. To create a CRC handle from a polynom pass it along with the calculation options to the CRCCreate. If the CRC handle is not longer used, the handle can be freed by DestroyCRC, if the handle was not allocated statically.

a. initialize CRC by providig necessary details:
CRChandle_t *CRCCreate(uint8_t CRCbits, CRC_t Polynom, CRC_t Init, bool RefIn, bool RefOut, CRC_t XOrOut)
CRCbits: Number of bits for CRC value. Supported values are 1 to 64.
Polynom: CRC polynom
Init: CRC initial value
RefIn: reflect bit order of input stream (true/ false)
RefOut: reflect CRC value (true/ false)
XOrOut: Xor CRC value

Function will fail, if number of crcbits are not supported or system does not provided enough memory to hold the CRChandle_t

b. initialize CRC by specifing a name (see source code for valid names ;-) ):
CRChandle_t *CRCCreateFromName(char *CRCname)
CRCname: name of CRC

Function will fail, if number of crcbits are not supported, name is not known or system does not provided enough memory to hold the CRChandle_t

Calculate CRC:
CRC_t CRC(CRChandle_t *CRChandle, uint8_t *Buffer, size_t Length)
CRChandle: handle of CRC
Buffer: data
Length: length of data
Dump CRC as C code to initialize a static CRC handle while compiling:
char *CRCdump(CRChandle_t *CRChandle)
CRChandle: handle of CRC

Function will return an allocated string.

Destroy a non static CRC handle
void CRCDestroy(CRChandle_t *CRChandle)
CRChandle: handle of CRC

example 1

#include "CRC.h"

static CRChandle_t *CRC_CCITT16 = NULL;

...
 
// create CRC table for smart message protocol (SML) once: 
//    16bits 
//    polynom is x^{16} + x^{12} + x^5 + 1
//    initial value: 0xffff
//    reverse input and output
//    toggle all output bits
if(!CRC_CCITT16)
    CRC_CCITT16 = CRCCreate(16, 0x1021, 0xffff, true, true, 0xffff);

...

CRC_t crc16;
// calculate CRC
crc16 = CRC(CRC_CCITT16, buf, len);

example 2

#include "CRC.h"

//    16bits 
//    polynom is x^{16} + x^{12} + x^5 + 1
//    CRC initial value: 0xffff
//    reflect input and output
//    toggle all output bits
static CRChandle_t CRC_CCITT16 = {
  .CRCbits = 16,
  .CRCpad = 0,
  .Polynom = 0x1021,
  .Init = 0xffff,
  .XOrOut = 0xffff,
  .RefIn = true,
  .RefOut = true,
  .Polymask = 0xffff,
  .Polytable = {
    0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf, 0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
    0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e, 0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
    0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd, 0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
    0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c, 0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
    0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb, 0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
    0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a, 0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
    0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9, 0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
    0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738, 0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
    0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7, 0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
    0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036, 0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
    0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5, 0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
    0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134, 0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
    0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3, 0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
    0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232, 0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
    0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1, 0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
    0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330, 0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
  }};

...
CRC_t crc16;

// calculate CRC
crc16 = CRC(&CRC_CCITT16, buf, len);

example 3

#include "CRC.h"

...
        
CRChandle_t *CRC_CCITT16;
char *ccode;

// create CRC table for smart message protocol (SML): 
//    16bits 
//    polynom is x^{16} + x^{12} + x^5 + 1
//    initial value: 0xffff
//    reverse input and output
//    toggle all output bits
CRC_CCITT16 = CRCCreate(16, 0x1021, 0xffff, true, true, 0xffff);

// dump the CRC
ccode = CRCdump(CRC_CCITT16);
ESP_LOGI("CRC", "%s", ccode);

// cleanup
free(ccode);
CRCDestroy(CRC_CCITT16);