WireCrc.h

#ifndef WireCrc_h
#define WireCrc_h
#include <stdint.h>

class WireCrc {
  public:
    WireCrc() {}
    /**
       Starts a new CRC8 calculation.
       @param data      byte array
       @param length    number of bytes
       @return uint8_t  crc
    */
    uint8_t calc(uint8_t *data, unsigned int length) {
      seed = 0;
      return update(data, length);
    }
    /**
       Feed more data in the CRC calculation. calc() must
       be called the first time, before using update()
       multiple times.
       @param data      byte array
       @param length    number of bytes
       @return uint8_t  crc
    */
    uint8_t update(uint8_t *data, unsigned int length) {
      uint8_t crc = seed;
      uint8_t extract;
      uint8_t sum;
      for (unsigned int i = 0; i < length; i++) {
        extract = *data;
        for (char j = 8; j; j--) {
          sum = (crc ^ extract) & 0x01;
          crc >>= 1;
          if (sum) {
            crc ^= 0x8C;
          }
          extract >>= 1;
        }
        data++;
      }
      return crc;
    }
  private:
    uint8_t seed = 0;
};
#endif