crc32

(PHP 4 >= 4.0.1, PHP 5)

crc32 — 文字列の crc32 多項式計算を行う

説明

int crc32 ( string str )

strの32ビット長のCRC(cyclic redundancy checksum)チェックサムを生成します。これは、受信されたデータの整合性を検証するために通常使用されます。

なぜなら、PHP の整数型は符号付きで、多くの crc32 チェックサムは負の整数になるためで、符号なしの crc32 チェックサムの文字列表記を取得するには sprintf() もしくは printf() の "%u" フォーマッタを使用する必要があります。

この 2 番目の例は printf() 関数を用いた変換後のチェックサムの表示方法を示しています。

例 2256. crc32 チェックサムの表示


<?php

$checksum = crc32("The quick brown fox jumped over the lazy dog.");

printf("%u\n", $checksum);

?>

md5(), sha1() も参照ください。

add a note User Contributed Notes
crc32

adam dot chout at gmail dot com
06-Mar-2007 06:25


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

roberto at spadim dot com dot br
08-Apr-2006 01:52


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));

}

Bulk at bulksplace dot com
27-Aug-2005 09:46


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: 



<?

// $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.

schmeic-php at lovo dot org
08-Jul-2005 05:26


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;

}



?>

gribber (_at) hellburner (dot_) net
19-May-2004 06:41


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);

}

?>

waldomonster at netjukebox dot demon dot nl
24-Apr-2004 12:48


<?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 12:44


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 10:27


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 11:12


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";

?>

quix at free dot fr
06-May-2003 05:19


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;

    }

?>

lander at liebe dot nu
21-Apr-2003 11:22


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;


}


?>

spectrumizer at cycos dot net
30-Dec-2002 08:30


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

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Last updated: Mon, 05 Feb 2007