CRC8-Check in PHP

Question

How can I generate a CRC-8 checksum in PHP?

Answer 1

Have a look here: http://en.wikipedia.org/wiki/Computation_of_CRC

Answer 2

Does it have to be CRC8?

On PHP.net there is an really simple implementation of CRC16 and a native version of CRC32.

If it does have to be CRC8 I would recommend coding something from the sudo code on the wikipedia page Marius pointed out.

Answer 3

function crcnifull ($dato, $byte)
{
  static $PolyFull=0x8c;

  for ($i=0; $i<8; $i++)
  {
    $x=$byte&1;
    $byte>>=1;
    if ($dato&1) $byte|=0x80;
    if ($x) $byte^=$PolyFull;
    $dato>>=1;
  }
  return $byte;
}

function crc8 (array $ar,$n=false)
{
  if ($n===false) $n=count($ar);
  $crcbyte=0;
  for ($i=0; $i<$n; $i++) $crcbyte=crcnifull($ar[$i], $crcbyte);
  return $crcbyte;
}

To use this function for a binary string you have to convert the binary string to an array first. That can be achieved like this:

function sbin2ar($sbin)
{
  $ar=array();
  $ll=strlen($sbin);
  for ($i=0; $i<$ll; $i++) $ar[]=ord(substr($sbin,$i,1));
  return $ar;
}

Example how to use the whole thing:

$crc8=crc8(sbin2ar($packet));