EEPROM CRC

/***

    Written by Christopher Andrews.

    CRC algorithm generated by pycrc, MIT licence ( https://github.com/tpircher/pycrc ).

    A CRC is a simple way of checking whether data has changed or become corrupted.

    This example calculates a CRC value directly on the EEPROM values.

    The purpose of this example is to highlight how the EEPROM object can be used just like an array.

***/

#include <Arduino.h>
#include <EEPROM.h>

void setup() {

  //Start serial

  Serial.begin(9600);

  while (!Serial) {

    ; // wait for serial port to connect. Needed for native USB port only

  }

  //Print length of data to run CRC on.

  Serial.print("EEPROM length: ");

  Serial.println(EEPROM.length());

  //Print the result of calling eeprom_crc()

  Serial.print("CRC32 of EEPROM data: 0x");

  Serial.println(eeprom_crc(), HEX);

  Serial.print("\n\nDone!");
}

void loop() {

  /* Empty loop */
}

unsigned long eeprom_crc(void) {

  const unsigned long crc_table[16] = {

    0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac,

    0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c,

    0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c,

    0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c

  };

  unsigned long crc = ~0L;

  for (int index = 0 ; index < EEPROM.length()  ; ++index) {

    crc = crc_table[(crc ^ EEPROM[index]) & 0x0f] ^ (crc >> 4);

    crc = crc_table[(crc ^ (EEPROM[index] >> 4)) & 0x0f] ^ (crc >> 4);

    crc = ~crc;

  }

  return crc;
}