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PHP : Function Reference : String Functions : crc32

crc32

Calculates the crc32 polynomial of a string (PHP 4 >= 4.0.1, PHP 5)
int crc32 ( string str )

Example 2402. Displaying a crc32 checksum

This example shows how to print a converted checksum with the printf() function:

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<?php
$checksum = crc32("The quick brown fox jumped over the lazy dog.");
printf("%u\n", $checksum);
?>

Code Examples / Notes » crc32

xethmir
This is a really simple way of displaying the crc-32 hexadecimal code/checksum for a file... (absolute paths are more reliable)
<?
$file = "http://foo.net/bar.jpg";
// Read the file into an array
$data = file($file);
// Join the array into a string
$data = implode('', $data);
// Calculate the crc
$crc = crc32($data);
//convert from decimal to hexadecimal
$crchex=DecHex($crc*1);
//echo the result
echo "$crchex";
?>

arachnid
Note that the CRC32 algorithm should NOT be used for cryptographic purposes, or in situations where a hostile/untrusted user is involved, as it is far too easy to generate a hash collision for CRC32 (two different binary strings that have the same CRC32 hash). Instead consider SHA-1 or MD5.

roberto
MODBUS RTU, CRC16,
input-> modbus rtu string
output -> 2bytes string, in correct modbus order
function crc16($string,$length=0){
$auchCRCHi=array( 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81,
0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0,
0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01,
0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41,
0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81,
0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0,
0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01,
0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,
0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81,
0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0,
0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01,
0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,
0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81,
0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0,
0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01,
0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,
0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81,
0x40);
$auchCRCLo=array( 0x00, 0xC0, 0xC1, 0x01, 0xC3, 0x03, 0x02, 0xC2, 0xC6, 0x06, 0x07, 0xC7, 0x05, 0xC5, 0xC4,
0x04, 0xCC, 0x0C, 0x0D, 0xCD, 0x0F, 0xCF, 0xCE, 0x0E, 0x0A, 0xCA, 0xCB, 0x0B, 0xC9, 0x09,
0x08, 0xC8, 0xD8, 0x18, 0x19, 0xD9, 0x1B, 0xDB, 0xDA, 0x1A, 0x1E, 0xDE, 0xDF, 0x1F, 0xDD,
0x1D, 0x1C, 0xDC, 0x14, 0xD4, 0xD5, 0x15, 0xD7, 0x17, 0x16, 0xD6, 0xD2, 0x12, 0x13, 0xD3,
0x11, 0xD1, 0xD0, 0x10, 0xF0, 0x30, 0x31, 0xF1, 0x33, 0xF3, 0xF2, 0x32, 0x36, 0xF6, 0xF7,
0x37, 0xF5, 0x35, 0x34, 0xF4, 0x3C, 0xFC, 0xFD, 0x3D, 0xFF, 0x3F, 0x3E, 0xFE, 0xFA, 0x3A,
0x3B, 0xFB, 0x39, 0xF9, 0xF8, 0x38, 0x28, 0xE8, 0xE9, 0x29, 0xEB, 0x2B, 0x2A, 0xEA, 0xEE,
0x2E, 0x2F, 0xEF, 0x2D, 0xED, 0xEC, 0x2C, 0xE4, 0x24, 0x25, 0xE5, 0x27, 0xE7, 0xE6, 0x26,
0x22, 0xE2, 0xE3, 0x23, 0xE1, 0x21, 0x20, 0xE0, 0xA0, 0x60, 0x61, 0xA1, 0x63, 0xA3, 0xA2,
0x62, 0x66, 0xA6, 0xA7, 0x67, 0xA5, 0x65, 0x64, 0xA4, 0x6C, 0xAC, 0xAD, 0x6D, 0xAF, 0x6F,
0x6E, 0xAE, 0xAA, 0x6A, 0x6B, 0xAB, 0x69, 0xA9, 0xA8, 0x68, 0x78, 0xB8, 0xB9, 0x79, 0xBB,
0x7B, 0x7A, 0xBA, 0xBE, 0x7E, 0x7F, 0xBF, 0x7D, 0xBD, 0xBC, 0x7C, 0xB4, 0x74, 0x75, 0xB5,
0x77, 0xB7, 0xB6, 0x76, 0x72, 0xB2, 0xB3, 0x73, 0xB1, 0x71, 0x70, 0xB0, 0x50, 0x90, 0x91,
0x51, 0x93, 0x53, 0x52, 0x92, 0x96, 0x56, 0x57, 0x97, 0x55, 0x95, 0x94, 0x54, 0x9C, 0x5C,
0x5D, 0x9D, 0x5F, 0x9F, 0x9E, 0x5E, 0x5A, 0x9A, 0x9B, 0x5B, 0x99, 0x59, 0x58, 0x98, 0x88,
0x48, 0x49, 0x89, 0x4B, 0x8B, 0x8A, 0x4A, 0x4E, 0x8E, 0x8F, 0x4F, 0x8D, 0x4D, 0x4C, 0x8C,
0x44, 0x84, 0x85, 0x45, 0x87, 0x47, 0x46, 0x86, 0x82, 0x42, 0x43, 0x83, 0x41, 0x81, 0x80,
0x40);
$length =($length<=0?strlen($string):$length);
$uchCRCHi =0xFF;
$uchCRCLo =0xFF;
$uIndex =0;
for ($i=0;$i<$length;$i++){
$uIndex =$uchCRCLo ^ ord(substr($string,$i,1));
$uchCRCLo =$uchCRCHi ^ $auchCRCHi[$uIndex];
$uchCRCHi =$auchCRCLo[$uIndex] ;
}
return(chr($uchCRCLo).chr($uchCRCHi));
}

adam dot chout
it should be poitned out that this function does not operate the same on 32-bit systems and 64-bit systems. so any php code written for one is not portable on the other. more information can be found here:
http://bugs.php.net/bug.php?id=39062

manuel
In response to quix at free dot fr (http://www.php.net/manual/de/function.crc32.php#31832):
Through buffering his CRC32 calculation is about 2-4 times faster:
<?php
 function __crc32_file($name)
 {
   // Creates a CRC from a file
   // Info: look at __crc32_string
   
   global $__crc32_table;
   // Start out with all bits set high.
   $crc = 0xffffffff;
   // Open the file
   $fp = fopen($name, "rb");
   
   // Read the file using a 1MB buffer
   // This will speed up CRC calculation at least 2-4x!
   // (5MB file: 15sec instead of 50sec)
   if ($fp != false)
   {
     $buffer = '';
     
     while (!feof($fp))
     {
       $buffer = fread($fp, 1048576); // Buffer 1MByte of file into memory
       $len = strlen($buffer);        // Cache buffer length (just this saves about 10sec on a 5MB file!)
       for ($i = 0; $i < $len; $i++)
       {
         $crc = (($crc >> 8) & 0x00ffffff) ^ $__crc32_table[($crc & 0xFF) ^ ord($buffer[$i])];
       }
     }
     fclose($fp);
   }
   // Exclusive OR the result with the beginning value.
   return $crc ^ 0xffffffff;
 }
?>

petteri
If you have php version<5.1.2 you might use this.
It's a little bit faster than __crc32_file() :)
Ps. crc32_combine() is ported directly from zlib.
<?php
function crc32_file($filename)
{
$fp=fopen($filename, "rb");
$old_crc=false;
if ($fp != false) {
$buffer = '';

while (!feof($fp)) {
$buffer=fread($fp, 10485760);
$len=strlen($buffer);      
$t=crc32($buffer);

if ($old_crc) {
$crc32=crc32_combine($old_crc, $t, $len);
$old_crc=$crc32;
} else {
$crc32=$old_crc=$t;
}
}
fclose($fp);
} else {
print "Cannot open file\n";
}
return $crc32;
}
function crc32_combine($crc1, $crc2, $len2)
{
$odd[0]=0xedb88320;
$row=1;
for($n=1;$n<32;$n++) {
$odd[$n]=$row;
$row<<=1;
}
gf2_matrix_square($even,$odd);
gf2_matrix_square($odd,$even);
do {
/* apply zeros operator for this bit of len2 */
gf2_matrix_square($even, $odd);
if ($len2 & 1)
$crc1=gf2_matrix_times($even, $crc1);
$len2>>=1;

/* if no more bits set, then done */
if ($len2==0)
break;

/* another iteration of the loop with odd and even swapped */
gf2_matrix_square($odd, $even);
if ($len2 & 1)
$crc1=gf2_matrix_times($odd, $crc1);
$len2>>= 1;

} while ($len2 != 0);
$crc1 ^= $crc2;
return $crc1;
}
function gf2_matrix_square(&$square, &$mat)
{
for ($n=0;$n<32;$n++) {
$square[$n]=gf2_matrix_times($mat, $mat[$n]);
}
}
function gf2_matrix_times($mat, $vec)
{
$sum=0;
$i=0;
while ($vec) {
if ($vec & 1) {
$sum ^= $mat[$i];
}
$vec>>= 1;
$i++;
}
return $sum;
}
?>

mail
I used the abs value of this function on a 32-bit system. When porting the code to a 64-bit system I’ve found that the value is different. The following code has the same outcome on both systems.
<?php
  $crc = abs(crc32($string));
  if( $crc & 0x80000000){
     $crc ^= 0xffffffff;
     $crc += 1;
  }
  /* Old solution
   * $crc = abs(crc32($string))
   */
?>

schmeic-php
I think that Mario's (spectrumizer at cycos dot net) CRC16 algorithm might be wrong.  At least according to these two online calculators:
http://www.zorc.breitbandkatze.de/crc.html
http://www.lammertbies.nl/comm/info/crc-calculation.html
 However, it seems that there can be some confusion concerning "official" CRC16 algorithms.  See this article for two possible CRC16-CCITT algorithms:
http://www.joegeluso.com/software/articles/ccitt.htm
 Here is a php implementation of the "bad" CRC16-CCITT algorithm from the article.  The "bad" implementation might not match the "official" algorithm, but is widely used, including by the two crc calculators mentioned above.
 Note that crc16-CCITT is also referred to as crc16c.
<?php
// this function is used to calculate the (common) crc16c for an entire buffer
function calculate_common_crc16c($buffer)
{
$crc16c = 0xffff;  // the crc initial value
$buffer_length = strlen($buffer);
   for ($i = 0; $i < $buffer_length; $i++)
   {
$ch = ord($buffer[$i]);
$crc16c = update_common_crc16c($ch, $crc16c);
   }
   return $crc16c;
}
// this function is used to calculate the (common) crc16c byte by byte
// $ch is the next byte and $crc16c is the result from the last call, or 0xffff initially
function update_common_crc16c($ch, $crc16c)
{
global $crc16c_polynomial;
   // This comment was in the code from
   // http://www.joegeluso.com/software/articles/ccitt.htm
   // Why are they shifting this byte left by 8 bits??
   // How do the low bits of the poly ever see it?
   $ch <<= 8;
   for($i = 0; $i < 8; $i++)
   {
       if (($crc16c ^ $ch) & 0x8000)
       {
           $xor_flag = true;
       }
       else
       {
           $xor_flag = false;
       }
       $crc16c = $crc16c << 1;
       if ($xor_flag)
       {
           $crc16c = $crc16c ^ $crc16c_polynomial;
       }
       $ch = $ch << 1;
   }
// mask off (zero out) the upper two bytes
$crc16c = $crc16c & 0x0000ffff;
   return $crc16c;
}
?>

slimshady451
I see a lot of function for crc32_file, but for php version >= 5.1.2 don't forget you can use this :
function crc32_file($filename)
{
return hash_file ('CRC32', $filename , FALSE );
}
Using crc32(file_get_contents($filename)) will use too many memory on big file so don't use it.

quix
I needed the crc32 of a file that was pretty large, so I didn't want to read it into memory.
So I made this:
<?php
$GLOBALS['__crc32_table']=array(); // Lookup table array
__crc32_init_table();
function __crc32_init_table() { // Builds lookup table array
// This is the official polynomial used by
// CRC-32 in PKZip, WinZip and Ethernet.
$polynomial = 0x04c11db7;
// 256 values representing ASCII character codes.
for($i=0;$i <= 0xFF;++$i) {
$GLOBALS['__crc32_table'][$i]=(__crc32_reflect($i,8) << 24);
for($j=0;$j < 8;++$j) {
$GLOBALS['__crc32_table'][$i]=(($GLOBALS['__crc32_table'][$i] << 1) ^
(($GLOBALS['__crc32_table'][$i] & (1 << 31))?$polynomial:0));
}
$GLOBALS['__crc32_table'][$i] = __crc32_reflect($GLOBALS['__crc32_table'][$i], 32);
}
}
function __crc32_reflect($ref, $ch) { // Reflects CRC bits in the lookup table
$value=0;

// Swap bit 0 for bit 7, bit 1 for bit 6, etc.
for($i=1;$i<($ch+1);++$i) {
if($ref & 1) $value |= (1 << ($ch-$i));
$ref = (($ref >> 1) & 0x7fffffff);
}
return $value;
}
function __crc32_string($text) { // Creates a CRC from a text string
// Once the lookup table has been filled in by the two functions above,
// this function creates all CRCs using only the lookup table.
// You need unsigned variables because negative values
// introduce high bits where zero bits are required.
// PHP doesn't have unsigned integers:
// I've solved this problem by doing a '&' after a '>>'.
// Start out with all bits set high.
$crc=0xffffffff;
$len=strlen($text);
// Perform the algorithm on each character in the string,
// using the lookup table values.
for($i=0;$i < $len;++$i) {
$crc=(($crc >> 8) & 0x00ffffff) ^ $GLOBALS['__crc32_table'][($crc & 0xFF) ^ ord($text{$i})];
}

// Exclusive OR the result with the beginning value.
return $crc ^ 0xffffffff;
}

function __crc32_file($name) { // Creates a CRC from a file
// Info: look at __crc32_string
// Start out with all bits set high.
$crc=0xffffffff;
if(($fp=fopen($name,'rb'))===false) return false;
// Perform the algorithm on each character in file
for(;;) {
$i=@fread($fp,1);
if(strlen($i)==0) break;
$crc=(($crc >> 8) & 0x00ffffff) ^ $GLOBALS['__crc32_table'][($crc & 0xFF) ^ ord($i)];
}

@fclose($fp);

// Exclusive OR the result with the beginning value.
return $crc ^ 0xffffffff;
}
?>

spectrumizer
Here is a tested and working CRC16-Algorithm:
<?php
function crc16($string) {
 $crc = 0xFFFF;
 for ($x = 0; $x < strlen ($string); $x++) {
   $crc = $crc ^ ord($string[$x]);
   for ($y = 0; $y < 8; $y++) {
     if (($crc & 0x0001) == 0x0001) {
       $crc = (($crc >> 1) ^ 0xA001);
     } else { $crc = $crc >> 1; }
   }
 }
 return $crc;
}
?>
Regards,
Mario

ren
Dealing with 32 bit unsigned values overflowing 32 bit php signed values can be done by adding 0x10000000 to any unexpected negative result, rather than using sprintf.
$i = crc32('1');
printf("%u\n", $i);
if (0 > $i)
{
   // Implicitly casts i as float, and corrects this sign.
   $i += 0x100000000;
}
var_dump($i);
Outputs:
2212294583
float(2212294583)

same
bit by bit crc32 computation
<?php
function bitbybit_crc32($str,$first_call=false){
//reflection in 32 bits of crc32 polynomial 0x04C11DB7
$poly_reflected=0xEDB88320;
//=0xFFFFFFFF; //keep track of register value after each call
static $reg=0xFFFFFFFF;
//initialize register on first call
if($first_call) $reg=0xFFFFFFFF;

$n=strlen($str);
$zeros=$n<4 ? $n : 4;
//xor first $zeros=min(4,strlen($str)) bytes into the register
for($i=0;$i<$zeros;$i++)
$reg^=ord($str{$i})<<$i*8;
//now for the rest of the string
for($i=4;$i<$n;$i++){
$next_char=ord($str{$i});
for($j=0;$j<8;$j++)
$reg=(($reg>>1&0x7FFFFFFF)|($next_char>>$j&1)<<0x1F)
^($reg&1)*$poly_reflected;
}
//put in enough zeros at the end
for($i=0;$i<$zeros*8;$i++)
$reg=($reg>>1&0x7FFFFFFF)^($reg&1)*$poly_reflected;
//xor the register with 0xFFFFFFFF
return ~$reg;
}
$str="123456789"; //whatever
$blocksize=4; //whatever
for($i=0;$i<strlen($str);$i+=$blocksize) $crc=bitbybit_crc32(substr($str,$i,$blocksize),!$i);
?>

lander
A simple and quite fast (10ms/Mb) way to generate checksums used with the popular SFV (Simple File Verification) format. strtoupper() isn't really needed, but the output looks better this way ;)
<?php
function generate_sfv_checksum($filename) {
 $sfv_checksum = strtoupper(dechex(crc32(file_get_contents($filename))));
 return $sfv_checksum;
}
?>

gribber _at hellburner dot_ net
A little correction to the sfv checksum code above, this was confuseing me for a while, heading zeros was striped away.
<?php
function sfv_checksum ($filename) {
   return str_pad (strtoupper (dechex (crc32 (file_get_contents ($filename)))), 8, '0', STR_PAD_LEFT);
}
?>

bulk
A faster way I've found to return CRC values of larger files, is instead of using the file()/implode() method used below, is to us file_get_contents() (PHP 4 >= 4.3.0) which uses memory mapping techniques if supported by your OS to enhance performance. Here's my example function:
<?
// $file is the path to the file you want to check.
function file_crc($file)
{
   $file_string = file_get_contents($file);
   $crc = crc32($file_string);

   return sprintf("%u", $crc);
}
$file_to_crc = /home/path/to/file.jpg;
echo file_crc($file_to_crc); // Outputs CRC value for given file.
?>
I've found in testing this method is MUCH faster for larger binary files.

waldomonster
<?php
$data = 'dot';
echo dechex(crc32($data));
?>
Returns 59278a3
Witch is missing a leading zero.
<?php
$data = 'dot';
echo str_pad(dechex(crc32($data)), 8, '0', STR_PAD_LEFT);
?>
Returns the correct string: 059278a3

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