PHP define function CALCULATE CRC-16 CCITT

DO anyone have a php function that will calculate CRC-16 CCITT checksum using the selected region.

 

Check the comments on this page:

http://php.net/manual/en/function.crc32.php

Should help you out.

 

Try these:

<?php
// CCITT, X24
define(CRC16POLYN,0x1021);
define(CRC16POLYI,0x8408);

// for "STANDARD" use 0x8005 and 0xA001

function CRC16Normal($buffer) {
	$result = 0xFFFF;
	if ( ($length = strlen($buffer)) > 0) {
		for ($offset = 0; $offset < $length; $offset++) {
			$result ^= (ord($buffer[$offset]) << 8);
			for ($bitwise = 0; $bitwise < 8; $bitwise++) {
				if (($result <<= 1) & 0x10000) $result ^= CRC16POLYN;
				$result &= 0xFFFF; /* gut the overflow as php has no 16 bit types */
			}
		}
	}
	return $result;
}

function CRC16Inverse($buffer) {
	$result = 0xFFFF;
	if ( ($length = strlen($buffer)) > 0) {
		for ($offset = 0; $offset < $length; $offset++) {
			$result ^= ord($buffer[$offset]);
			for ($bitwise = 0; $bitwise < 8; $bitwise++) {
				$lowBit = $result & 0x0001;
				$result >>= 1;
				if ($lowBit) $result ^= CRC16POLYI;
			}
		}
	}
	return $result;
}


echo '
	0x',dechex(CRC16Normal('123456789')),' == 0x29B1<br />
	0x',dechex(CRC16Normal('abc')),' == 0x514A<br />
	0x',dechex(CRC16Normal('ABC')),' == 0xF508<br />
	0x',dechex(CRC16Normal('This is a string')),' == 0x4BE9<br />
	<br />
	0x',dechex(CRC16Inverse('123456789')),' == 0x29B1<br />
	0x',dechex(CRC16Inverse('abc')),' == 0x514A<br />
	0x',dechex(CRC16Inverse('ABC')),' == 0xF508<br />
	0x',dechex(CRC16Inverse('This is a string')),' == 0x4BE9<br />';
?>

Code (markup):

Should work good for you... and another of those routines that I really wish higher level languages gave you access to the carry flag on the processor

Gave you both methods of reaching the same number -- just to show how it's done.

 

This works as well and its shorter

<?php
function crc16($data)
 {
   $crc = 0xFFFF;
   for ($i = 0; $i < strlen($data); $i++)
   {
     $x = (($crc >> 8) ^ ord($data[$i])) & 0xFF;
     $x ^= $x >> 4;
     $crc = (($crc << 8) ^ ($x << 12) ^ ($x << 5) ^ $x) & 0xFFFF;
   }
   return $crc;
 }
?>

Code (markup):

 

Polynomial's hard coded though --- though it's a good trade when you only need CCITT and speed is more important than versatility.

 

hello@community,

I have a question to this old post. First, THANKS for the code
I have a message in hex "80 00 00 03" crc-ccitt kermit. The checksum (checked with lammertbies.nl) is "f5 1f". When I use the the php-code above, I did not get that checksum. I know, that I do not have to use the polynom 0x1021. The right polynom is the revers one 0x8408. Also the result is not the right one for me. The correct result is "$result = 0x0000" instead of "$result = 0xFFFF". But that does not solve the problem. I did not get the right checksum for my message "80 00 00 03".
Do I have to change the php-code or what is the error? Please help me