byte - Calculate CRC with words (16-bit) as a base variable -

is there simple crc algorithm based on lookup table, words entering algorithm instead of bytes.

for example, algorithm works bytes:

#include <stdint.h>  const uint16_t wtable_crc16_modbus[256] = {     0x0000, 0xc0c1, 0xc181, 0x0140, 0xc301, 0x03c0, 0x0280, 0xc241, 0xc601, 0x06c0, 0x0780, 0xc741, 0x0500, 0xc5c1, 0xc481, 0x0440,     0xcc01, 0x0cc0, 0x0d80, 0xcd41, 0x0f00, 0xcfc1, 0xce81, 0x0e40, 0x0a00, 0xcac1, 0xcb81, 0x0b40, 0xc901, 0x09c0, 0x0880, 0xc841,     0xd801, 0x18c0, 0x1980, 0xd941, 0x1b00, 0xdbc1, 0xda81, 0x1a40, 0x1e00, 0xdec1, 0xdf81, 0x1f40, 0xdd01, 0x1dc0, 0x1c80, 0xdc41,     0x1400, 0xd4c1, 0xd581, 0x1540, 0xd701, 0x17c0, 0x1680, 0xd641, 0xd201, 0x12c0, 0x1380, 0xd341, 0x1100, 0xd1c1, 0xd081, 0x1040,     0xf001, 0x30c0, 0x3180, 0xf141, 0x3300, 0xf3c1, 0xf281, 0x3240, 0x3600, 0xf6c1, 0xf781, 0x3740, 0xf501, 0x35c0, 0x3480, 0xf441,     0x3c00, 0xfcc1, 0xfd81, 0x3d40, 0xff01, 0x3fc0, 0x3e80, 0xfe41, 0xfa01, 0x3ac0, 0x3b80, 0xfb41, 0x3900, 0xf9c1, 0xf881, 0x3840,     0x2800, 0xe8c1, 0xe981, 0x2940, 0xeb01, 0x2bc0, 0x2a80, 0xea41, 0xee01, 0x2ec0, 0x2f80, 0xef41, 0x2d00, 0xedc1, 0xec81, 0x2c40,     0xe401, 0x24c0, 0x2580, 0xe541, 0x2700, 0xe7c1, 0xe681, 0x2640, 0x2200, 0xe2c1, 0xe381, 0x2340, 0xe101, 0x21c0, 0x2080, 0xe041,     0xa001, 0x60c0, 0x6180, 0xa141, 0x6300, 0xa3c1, 0xa281, 0x6240, 0x6600, 0xa6c1, 0xa781, 0x6740, 0xa501, 0x65c0, 0x6480, 0xa441,     0x6c00, 0xacc1, 0xad81, 0x6d40, 0xaf01, 0x6fc0, 0x6e80, 0xae41, 0xaa01, 0x6ac0, 0x6b80, 0xab41, 0x6900, 0xa9c1, 0xa881, 0x6840,     0x7800, 0xb8c1, 0xb981, 0x7940, 0xbb01, 0x7bc0, 0x7a80, 0xba41, 0xbe01, 0x7ec0, 0x7f80, 0xbf41, 0x7d00, 0xbdc1, 0xbc81, 0x7c40,     0xb401, 0x74c0, 0x7580, 0xb541, 0x7700, 0xb7c1, 0xb681, 0x7640, 0x7200, 0xb2c1, 0xb381, 0x7340, 0xb101, 0x71c0, 0x7080, 0xb041,     0x5000, 0x90c1, 0x9181, 0x5140, 0x9301, 0x53c0, 0x5280, 0x9241, 0x9601, 0x56c0, 0x5780, 0x9741, 0x5500, 0x95c1, 0x9481, 0x5440,     0x9c01, 0x5cc0, 0x5d80, 0x9d41, 0x5f00, 0x9fc1, 0x9e81, 0x5e40, 0x5a00, 0x9ac1, 0x9b81, 0x5b40, 0x9901, 0x59c0, 0x5880, 0x9841,     0x8801, 0x48c0, 0x4980, 0x8941, 0x4b00, 0x8bc1, 0x8a81, 0x4a40, 0x4e00, 0x8ec1, 0x8f81, 0x4f40, 0x8d01, 0x4dc0, 0x4c80, 0x8c41,     0x4400, 0x84c1, 0x8581, 0x4540, 0x8701, 0x47c0, 0x4680, 0x8641, 0x8201, 0x42c0, 0x4380, 0x8341, 0x4100, 0x81c1, 0x8081, 0x4040 };  uint16_t modbus_calculate_crc16(uint8_t *frame, uint8_t size) {     // initialize crc16 word     uint16_t crc16 = 0xffff;      // calculate crc16 word     uint16_t ind;     while(size--) {         ind = ( crc16 ^ *frame++ ) & 0x00ff;         crc16 >>= 8;         crc16 ^= wtable_crc16_modbus[ind];     }      // swap low , high bytes     crc16 = (crc16<<8) | (crc16>>8);      // return crc16 word     // swapped low , high bytes     return crc16; } 

since i'm going send words, using above algorithm need break each word in lsb , msb , repeat code in loop body twice, first lsb , msb. instead of doing that, update crc in 1 step, word algorithm (loop body) input.

if , if read words memory in little-endian order (least significant byte first), can read 16-bit word @ time. still need use table twice process word. loop be:

    size >>= 1;                     // better have been even!     uint16_t const *words = frame;  // better little-endian!     while (size--) {         crc16 ^= *words++;         crc16 = (crc16 >> 8) ^ wtable_crc16_modbus[crc16 & 0xff];         crc16 = (crc16 >> 8) ^ wtable_crc16_modbus[crc16 & 0xff];     } 

depending on processor, may need make sure frame points address. note if size odd, won't process last byte. if size can , odd, can add processing of last byte after loop.

if single table lookup per word, you'll need bigger table. existing table crc of single-byte values 0..255 (where initial crc zero, not 0xffff). bigger table same thing, two-byte values 0..65536, least significant byte processed first. can make table using existing table:

void modbus_bigtable(uint16_t *table) {     (uint16_t lo = 0; lo < 256; lo++) {         uint16_t crclo = wtable_crc16_modbus[lo];         uint16_t crchi = crclo >> 8;         crclo &= 0xff;         uint16_t *nxt = table;         (uint16_t hi = 0; hi < 256; hi++) {             *nxt = crchi ^ wtable_crc16_modbus[hi ^ crclo];             nxt += 256;         }         table++;     } } 

then loop becomes:

    size >>= 1;                     // better have been even!     uint16_t const *words = frame;  // better little-endian!     while (size--)         crc16 = table[crc16 ^ *words++];