字符串函数
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crc32

(PHP 4 >= 4.0.1, PHP 5)

crc32 — 计算一个字符串的 crc32 多项式

说明

int crc32 ( string $str )

生成 str 的 32 位循环冗余校验码多项式。这通常用于检查传输的数据是否完整。

由于 PHP 的整数是带符号的，许多 crc32 校验码将返回负整数，因此你需要使用 sprintf() 或 printf() 的“%u”格式符来获取表示无符号 crc32 校验码的字符串。

示例中的第二行演示了如何使用 printf() 函数转换校验码：

Example #1 显示 crc32 校验码

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

参见 md5() 和 sha1()。

字符串函数
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PHP手册 - N: 计算一个字符串的 crc32 多项式

用户评论:

sneskid at hotmail dot com (15-Mar-2012 05:24)

On two different servers I found that crc32() relates to hash(\&#039;crc32b\&#039;,)
This may be good to know if you are writing a crc32_file function based on hash_file.
(The example does not compensate for negative crc32 results)
&lt;?php
$val = \&#039;hello\&#039;;
var_dump(crc32($val) == ( \&#039;0x\&#039; . hash(\&#039;crc32b\&#039;, $val) ) ); // bool(true)
var_dump(crc32($val) == ( \&#039;0x\&#039; . hash(\&#039;crc32\&#039;, $val) ) ); // bool(false)
?&gt;

Also if you are looking for a way to reduce collisions and still keep the hash result small (smaller than say md5) you could get a nice database friendly 64 bit value by using hash/crc32 and hash/crc32b, which is slower than a single md5 but the result may be more suitable for certain tasks.
&lt;?php
$val = \&#039;hello\&#039;;
$crc64 = ( \&#039;0x\&#039; . hash(\&#039;crc32\&#039;, $val) . hash(\&#039;crc32b\&#039;, $val) );
var_dump($crc64); // string(18) \&quot;0x3d6531193610a686\&quot;
var_dump($crc64 + 0); // int(4423996193312384646)
?&gt;

note: (\&#039;0x\&#039; . $hex . + 0) is faster than base_convert($hex,16,10)

alban dot lopez+php [ at ] gmail dot com (27-Nov-2011 02:02)

I made this code to verify Transmition with Vantage Pro2 ( weather station ) based on CRC16-CCITT standard.

<?php
// CRC16-CCITT validator
$crc_table = array(
    0x0,  0x1021,  0x2042,  0x3063,  0x4084,  0x50a5,  0x60c6,  0x70e7,
        0x8108,  0x9129,  0xa14a,  0xb16b,  0xc18c,  0xd1ad,  0xe1ce,  0xf1ef,
        0x1231,  0x210,  0x3273,  0x2252,  0x52b5,  0x4294,  0x72f7,  0x62d6,
        0x9339,  0x8318,  0xb37b,  0xa35a,  0xd3bd,  0xc39c,  0xf3ff,  0xe3de,
        0x2462,  0x3443,  0x420,  0x1401,  0x64e6,  0x74c7,  0x44a4,  0x5485,
        0xa56a,  0xb54b,  0x8528,  0x9509,  0xe5ee,  0xf5cf,  0xc5ac,  0xd58d,
        0x3653,  0x2672,  0x1611,  0x630,  0x76d7,  0x66f6,  0x5695,  0x46b4,
        0xb75b,  0xa77a,  0x9719,  0x8738,  0xf7df,  0xe7fe,  0xd79d,  0xc7bc,
        0x48c4,  0x58e5,  0x6886,  0x78a7,  0x840,  0x1861,  0x2802,  0x3823,
        0xc9cc,  0xd9ed,  0xe98e,  0xf9af,  0x8948,  0x9969,  0xa90a,  0xb92b,
        0x5af5,  0x4ad4,  0x7ab7,  0x6a96,  0x1a71,  0xa50,  0x3a33,  0x2a12,
        0xdbfd,  0xcbdc,  0xfbbf,  0xeb9e,  0x9b79,  0x8b58,  0xbb3b,  0xab1a,
        0x6ca6,  0x7c87,  0x4ce4,  0x5cc5,  0x2c22,  0x3c03,  0xc60,  0x1c41,
        0xedae,  0xfd8f,  0xcdec,  0xddcd,  0xad2a,  0xbd0b,  0x8d68,  0x9d49,
        0x7e97,  0x6eb6,  0x5ed5,  0x4ef4,  0x3e13,  0x2e32,  0x1e51,  0xe70,
        0xff9f,  0xefbe,  0xdfdd,  0xcffc,  0xbf1b,  0xaf3a,  0x9f59,  0x8f78,
        0x9188,  0x81a9,  0xb1ca,  0xa1eb,  0xd10c,  0xc12d,  0xf14e,  0xe16f,
        0x1080,  0xa1,  0x30c2,  0x20e3,  0x5004,  0x4025,  0x7046,  0x6067,
        0x83b9,  0x9398,  0xa3fb,  0xb3da,  0xc33d,  0xd31c,  0xe37f,  0xf35e,
        0x2b1,  0x1290,  0x22f3,  0x32d2,  0x4235,  0x5214,  0x6277,  0x7256,
        0xb5ea,  0xa5cb,  0x95a8,  0x8589,  0xf56e,  0xe54f,  0xd52c,  0xc50d,
        0x34e2,  0x24c3,  0x14a0,  0x481,  0x7466,  0x6447,  0x5424,  0x4405,
        0xa7db,  0xb7fa,  0x8799,  0x97b8,  0xe75f,  0xf77e,  0xc71d,  0xd73c,
        0x26d3,  0x36f2,  0x691,  0x16b0,  0x6657,  0x7676,  0x4615,  0x5634,
        0xd94c,  0xc96d,  0xf90e,  0xe92f,  0x99c8,  0x89e9,  0xb98a,  0xa9ab,
        0x5844,  0x4865,  0x7806,  0x6827,  0x18c0,  0x8e1,  0x3882,  0x28a3,
        0xcb7d,  0xdb5c,  0xeb3f,  0xfb1e,  0x8bf9,  0x9bd8,  0xabbb,  0xbb9a,
        0x4a75,  0x5a54,  0x6a37,  0x7a16,  0xaf1,  0x1ad0,  0x2ab3,  0x3a92,
        0xfd2e,  0xed0f,  0xdd6c,  0xcd4d,  0xbdaa,  0xad8b,  0x9de8,  0x8dc9,
        0x7c26,  0x6c07,  0x5c64,  0x4c45,  0x3ca2,  0x2c83,  0x1ce0,  0xcc1,
        0xef1f,  0xff3e,  0xcf5d,  0xdf7c,  0xaf9b,  0xbfba,  0x8fd9,  0x9ff8,
        0x6e17,  0x7e36,  0x4e55,  0x5e74,  0x2e93,  0x3eb2,  0xed1,  0x1ef0);

    $test = chr(0xC6).chr(0xCE).chr(0xA2).chr(0x03); // CRC16-CCITT = 0xE2B4
    genCRC ($test);
      
function genCRC (&$ptr)
{
    $crc = 0x0000;
    $crc_table = $GLOBALS['crc_table'];
    for ($i = 0; $i < strlen($ptr); $i++)
        $crc =  $crc_table[(($crc>>8) ^ ord($ptr[$i]))] ^ (($crc<<8) & 0x00FFFF);
    return $crc;
}
?>

arris at zsolttech dot com (19-Oct-2011 01:17)

not found anywhere crc64 based on http://bioinfadmin.cs.ucl.ac.uk/downloads/crc64/crc64.c .

(use gmp module)

<?php

/* OLDCRC */
define('POLY64REV', "d800000000000000");
define('INITIALCRC', "0000000000000000");
define('TABLELEN', 256);
/* NEWCRC */
// define('POLY64REV', "95AC9329AC4BC9B5");
// define('INITIALCRC', "FFFFFFFFFFFFFFFF");

if(function_exists('gmp_init')){
        class CRC64{

                private static $CRCTable = array();

                public static function encode($seq){

                        $crc = gmp_init(INITIALCRC, 16);
                        $init = FALSE;
                        $poly64rev = gmp_init(POLY64REV, 16);

                        if (!$init)
                        {
                                $init = TRUE;
                                for ($i = 0; $i < TABLELEN; $i++)
                                {
                                        $part = gmp_init($i, 10);
                                        for ($j = 0; $j < 8; $j++)
                                        {
                                                if (gmp_strval(gmp_and($part, "0x1")) != "0"){
                                                        // if (gmp_testbit($part, 1)){ /* PHP 5 >= 5.3.0, untested */
                                                        $part = gmp_xor(gmp_div_q($part, "2"), $poly64rev);
                                                } else {
                                                        $part = gmp_div_q($part, "2");
                                                }
                                        }
                                        self::$CRCTable[$i] = $part;
                                }
                        }

                        for($k = 0; $k < strlen($seq); $k++){
                                $tmp_gmp_val = gmp_init(ord($seq[$k]), 10);
                                $tableindex = gmp_xor(gmp_and($crc, "0xff"), $tmp_gmp_val);
                                $crc = gmp_div_q($crc, "256");
                                $crc = gmp_xor($crc, self::$CRCTable[gmp_strval($tableindex, 10)]);
                        }

                        $res = gmp_strval($crc, 16);

                        return $res;
                }
        }
} else {
        die("Please install php-gmp package!!!");
}
?>

sukitsupaluk at hotmail dot com (08-Sep-2011 11:04)

small sample convert crc32 to character map

<?php

function khash($data) {
    static $map="0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    $hash=crc32($data)+0x100000000;
    $str = "";
    do {
        $str = $map[31+ ($hash % 31)] . $str;
        $hash /= 31;
    } while($hash >= 1);    
    return $str;
}
$test= array(null,TRUE,FALSE,0,"0",1,"1","2","3","ab","abc","abcd","abcde","abcdefoo");
$out = array();
foreach($test as $s)
{
    $out[]=khash($s).": ". $s;
}
var_dump($out);

/*
output:
array
  0 => string 'zVvOYTv: ' (length=9)
  1 => string 'xKDKKL8: 1' (length=10)
  2 => string 'zVvOYTv: ' (length=9)
  3 => string 'zOKCQxh: 0' (length=10)
  4 => string 'zOKCQxh: 0' (length=10)
  5 => string 'xKDKKL8: 1' (length=10)
  6 => string 'xKDKKL8: 1' (length=10)
  7 => string 'AFSzIAO: 2' (length=10)
  8 => string 'BXGSvQJ: 3' (length=10)
  9 => string 'xZWOQSu: ab' (length=11)
  10 => string 'AVAwHOR: abc' (length=12)
  11 => string 'zKASNE1: abcd' (length=13)
  12 => string 'xLCTOV7: abcde' (length=14)
  13 => string 'zQLzKMt: abcdefoo' (length=17)

*/

?>

chernyshevsky at hotmail dot com (22-Sep-2010 11:54)

The crc32_combine() function provided by petteri at qred dot fi has a bug that causes an infinite loop, a shift operation on a 32-bit signed int might never reach zero. Replacing the function gf2_matrix_times() with the following seems to fix it:

<?php
function gf2_matrix_times($mat, $vec)
{
    $sum=0;
    $i=0;

    while ($vec) {
        if ($vec & 1) {
            $sum ^= $mat[$i];
        }
        $vec = ($vec >> 1) & 0x7FFFFFFF;
        $i++;      
    }
    return $sum;
}
?>

Otherwise, it's probably the best solution if you can't use hash_file(). Using a 1meg read buffer, the function only takes twice as long to process a 300meg files than hash_file() in my test.

gabri dot ns at gmail dot com (16-Sep-2010 06:05)

if you are looking for a fast function to hash a file, take a look at
http://www.php.net/manual/en/function.hash-file.php
this is crc32 file checker based on a CRC32 guide
it have performance at ~ 625 KB/s on my 2.2GHz Turion
far slower than hash_file('crc32b','filename.ext')
<?php
function crc32_file ($filename)
{
   $f = @fopen($filename,'rb');
   if (!$f) return false;
  
   static $CRC32Table, $Reflect8Table;
   if (!isset($CRC32Table))
   {
      $Polynomial = 0x04c11db7;
      $topBit = 1 << 31;
      
      for($i = 0; $i < 256; $i++)
      {
         $remainder = $i << 24;
         for ($j = 0; $j < 8; $j++)
         {
            if ($remainder & $topBit)
               $remainder = ($remainder << 1) ^ $Polynomial;
            else $remainder = $remainder << 1;
         }
        
         $CRC32Table[$i] = $remainder;
        
         if (isset($Reflect8Table[$i])) continue;
         $str = str_pad(decbin($i), 8, '0', STR_PAD_LEFT);
         $num = bindec(strrev($str));
         $Reflect8Table[$i] = $num;
         $Reflect8Table[$num] = $i;
      }
   }
  
   $remainder = 0xffffffff;
   while ($data = fread($f,1024))
   {
      $len = strlen($data);
      for ($i = 0; $i < $len; $i++)
      {
         $byte = $Reflect8Table[ord($data[$i])];
         $index = (($remainder >> 24) & 0xff) ^ $byte;
         $crc = $CRC32Table[$index];
         $remainder = ($remainder << 8) ^ $crc;
      }
   }
  
   $str = decbin($remainder);
   $str = str_pad($str, 32, '0', STR_PAD_LEFT);
   $remainder = bindec(strrev($str));
   return $remainder ^ 0xffffffff;
}
?>

<?php
$a = microtime();
echo dechex(crc32_file('filename.ext'))."\n";
$b = microtime();
echo array_sum(explode(' ',$b)) - array_sum(explode(' ',$a))."\n";
?>
Output:
ec7369fe
2.384134054184 (or similiar)

carlos at dimension-e dot net (27-Aug-2010 03:36)

This crc32 issue on 64 bits servers may not be a bug, but for sure it wracks many applications when the server migrates to a linux 64 bit machine.

For example, many database fields are set to accept signed 32 bits integers. This odd behavior makes those fields to be filled with the 2147483647 value, which es the higest possible number to be saved in this type of field.

It seems the PHP team regards this as a operative system issue, rather than a language issue, but the result is just the same: You just can not rely on this for data comparison between machines.

jian at theorchard dot com (17-Feb-2010 06:13)

This function returns an unsigned integer from a 64-bit Linux platform.  It does return the signed integer from other 32-bit platforms even a 64-bit Windows one.

The reason is because the two constants PHP_INT_SIZE and PHP_INT_MAX have different values on the 64-bit Linux platform.

I've created a work-around function to handle this situation.

<?php
function get_signed_int($in) {
    $int_max = pow(2, 31)-1;
    if ($in > $int_max){
        $out = $in - $int_max * 2 - 2;
    }
    else {
        $out = $in;
    }
    return $out;
}
?>

Hope this helps.

berna (at) gensis (dot) com (dot) br (30-Sep-2009 04:16)

For those who want a more familiar return value for the function:

<?php
function strcrc32($text) {
  $crc = crc32($text);
  if ($crc & 0x80000000) {
    $crc ^= 0xffffffff;
    $crc += 1;
    $crc = -$crc;
  }
  return $crc;
}
?>

And to show the result in Hex string:

<?php
function int32_to_hex($value) {
  $value &= 0xffffffff;
  return str_pad(strtoupper(dechex($value)), 8, "0", STR_PAD_LEFT);
}
?>

Anonymous (16-Jul-2009 09:26)

<?php
  echo crc32('example')+4294967296;
?>

gives you the same result as the CRC32() function in MySQL (>=4.1)

"SELECT CRC32('example')"

vice versa

"SELECT CRC32('example')-4294967296"

in MySQL gives you the same result as:

<?php
  echo  crc32('example');
?>

angelo (at) mandato (period) com (18-Jan-2008 02:54)

From my tests noted below, md5_file() function is the best function for performing file verification. This will remain the case until a native crc32_file() function is added to PHP.

file_crc() function that Bulk at bulksplace dot com posted is the most efficient solution on Windows for small and medium size files.  It is most likely because file_get_contents() uses memory mapping techniques.  Unfortunately on Linux (Fedora), the results were slightly better for md5_file().

sha1_file() on large files is slower than md5_file().  The time it takes for the __crc32_file() function found below is linear to the size of the file.  I would avoid using __crc32_file().  The file_crc() function will fail when using the file_get_contents() if the file is larger than the PHP.ini memory_limit setting.  Windows does not seem to use the memory_limit for file_get_contents(), but I did run into an error 'FATAL: emalloc(): Unable to allocate x bytes' when testing iso files.

I ran the following tests on both WindowsXP and Fedora 4 machines.

<?php
   // File verification tests by Angelo Mandato (angelo [at] mandato {period} com)
 
   // __crc32_file() is very slow, you can uncomment to test for yourself.
   //require_once('crc32_file.php');
   // Copy and paste the contents of the crc32_file() code found on
   // the php.net crc32 PHP manual page in a new file and save
   // as crc32_file.php in the same directory as this script.
 
   // Get microseconds
   function GetMicrotime()
   {
       list($usec, $sec) = explode(" ", microtime());
       return ((float)$usec + (float)$sec);
   }
 
   // file_crc() - function to test
   function file_crc($file)
   {
       $file_string = file_get_contents($file);
       $crc = crc32($file_string);
       return sprintf("%u", $crc);
   }

   $Methods = array('sha1_file()', 'md5_file()', 'file_crc()');
   if( function_exists('__crc32_file') )
       $Methods[] = '__crc32_file()';
   $directory = '/path/to/directory/'; // Don't forget trailing backslash.
   $files = scandir($directory);
 
   for( $method_index = 0; $method_index < count($Methods); $method_index++ )
   {
       $start_time = GetMicrotime();
       while( list($index,$file) = each($files) )
       {
           if( $file != '.' && $file != '..' && is_file($directory.$file) )
           {
               switch( $method_index )
               {
                   case 0: { // sha1_file()
                       $value = sha1_file($directory.$file);
                   }; break;
                   case 1: { // md5_file()
                       $value = md5_file($directory.$file);
                   }; break;
                   case 2: { // file_crc()
                       $value = file_crc($directory.$file);
                   }; break;
                   case 3: { // __crc32_file()
                       $value = __crc32_file($directory.$file);
                   }; break;
               }
           }
           else // It is not part of our test results, lets remove it from the array
           {
               unset($files[$index]);
           }
       }
       $end_time = GetMicrotime();
       echo sprintf("%s took %.03f seconds to calculate %d files.\n", $Methods[$method_index], $end_time-$start_time, count($files) );
       reset($files); // Reset pointer in array
   }
   echo "file verification tests completed.\n";
?>

It would be nice if a crc32_file() function was added to PHP natively.

I am not sure why anyone removed this post from this thread, but this is very useful information. and I believe it should remain.  If you're the moderator and deleted this before, please contact me and explain why it was removed. This is not a question, a report of a bug nor a feature request.  This is factual information that is useful to all.

dave at jufer dot info (03-Dec-2007 10:15)

This function returns the same int value on a 64 bit mc. like the crc32() function on a 32 bit mc.

<?php
function crcKw($num){
    $crc = crc32($num);
    if($crc & 0x80000000){
        $crc ^= 0xffffffff;
        $crc += 1;
        $crc = -$crc;
    }
    return $crc;
}
?>

Ren (03-Oct-2007 07:53)

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)

petteri at qred dot fi (29-Jun-2007 07:03)

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;
}
?>

slimshady451 (20-Jun-2007 10:14)

I see a lot of function for crc32_file, but for php version >= 5.1.2 don't forget you can use this :

<?php
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.

mail at tristansmis dot nl (30-May-2007 09:36)

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))
    */

?>

roberto at spadim dot com dot br (08-Apr-2006 05:52)

MODBUS RTU, CRC16,
input-> modbus rtu string
output -> 2bytes string, in correct modbus order

<?php
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));
}
?>

Bulk at bulksplace dot com (27-Aug-2005 01:46)

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:

<?php
// $file is the path to the file you want to check.
function file_crc($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 at netjukebox dot demon dot nl (23-Apr-2004 04:48)

<?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

arachnid at notdot dot net (14-Apr-2004 04:44)

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.

same (02-Feb-2004 01:27)

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);

?>

xethmir at yournextclient dot com (17-Jul-2003 03:12)

This is a really simple way of displaying the crc-32 hexadecimal code/checksum for a file... (absolute paths are more reliable)

<?php
$file = "http://example.com/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";
?>

quix at free dot fr (05-May-2003 09:19)

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 at cycos dot net (29-Dec-2002 11:30)

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