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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。

Warning

由于 PHP 的整数是带符号的，所以在 32 位系统上许多 crc32 校验码将返回负整数。尽管在 64 位上所有 crc32() 的结果将都是正整数。

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。

For a hexadecimal representation of the checksum you can either use the "%x" formatter of sprintf() or printf() or the dechex() conversion functions, both of these also take care of converting the crc32() result to an unsigned integer.

Having 64bit installations also return negative integers for higher result values was considered but would break the hexadecimal conversion as negatives would get an extra 0xFFFFFFFF######## offset then. As hexadecimal representation seems to be the most common use case we decided to not break this even if it breaks direct decimal comparisons in about 50% of the cases when moving from 32 to 64bits.

In retrospect having the function return an integer maybe wasn't the best idea and returning a hex string representation right away (as e.g. md5() does) might have been a better plan to begin with.

For a more portable solution you may also consider the generic hash() . hash("crc32b", $str) will return the same string as dechex(crc32($str)).

参数

str: 要校验的数据。

返回值

返回 str crc32 校验的整数。

范例

Example #1 显示一个 crc32 校验码

示例中的第二行演示了如何使用 printf() 函数转换校验码：

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

参见

hash() - 生成哈希值（消息摘要）
md5() - 计算字符串的 MD5 散列值
sha1() - 计算字符串的 sha1 散列值

用户评论:

[#1] JS at JavsSys dot Org [2013-04-13 16:22:06]

The khash() function by sukitsupaluk has two problems, it does not use all 62 characters from the $map set and when corrected it then produces different results on 64-bit compared to 32-bit PHP systems.

Here is my modified version :

<?php function khash($data) { static $map = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"; $hash = bcadd(sprintf('%u',crc32($data)) , 0x100000000); $str = ""; do { $str = $map[bcmod($hash, 62) ] . $str; $hash = bcdiv($hash, 62); } while ($hash >= 1); return $str; } //----------------------------------------------------------------------------------- $test = array(null, true, false, 0, "0", 1, "1", "2", "3", "ab", "abc", "abcd", "abcde", "abcdefoo", "248840027", "1365848013", // time() "9223372035488927794", // PHP_INT_MAX-time() "901131979", // mt_rand() "Sat, 13 Apr 2013 10:13:33 +0000" // gmdate('r') ); $out = array(); foreach ($test as $s) { $out[] = khash($s) . ": " . $s; } print "<h3>khash() -- maps a crc32 result into a (62-character) result</h3>"; print '<pre>'; var_dump($out); print "\n\n\$GLOBALS['raw_crc32']:\n"; var_dump($GLOBALS['raw_crc32']); print '</pre><hr>'; flush(); $pefile = __FILE__; print "<h3>$pefile</h3>"; ob_end_flush(); flush(); highlight_file($pefile); print "<hr>"; //----------------------------------------------------------------------------------- //----------------------------------------------------------------------------------- ?>

[#2] i at morfi dot ru [2013-03-18 13:16:33]

Implementation crc64() in php 64bit

<?php

function crc64Table()
{
    $crc64tab = [];

    // ECMA polynomial
    $poly64rev = (0xC96C5795 << 32) | 0xD7870F42;

    // ISO polynomial
    // $poly64rev = (0xD8 << 56);

    for ($i = 0; $i < 256; $i++)
    {
        for ($part = $i, $bit = 0; $bit < 8; $bit++) {
            if ($part & 1) {
                $part = (($part >> 1) & ~(0x8 << 60)) ^ $poly64rev;
            } else {
                $part = ($part >> 1) & ~(0x8 << 60);
            }
        }

       $crc64tab[$i] = $part;
    }

    return $crc64tab;
}

function crc64($string, $format = '%x')
{
    static $crc64tab;

    if ($crc64tab === null) {
        $crc64tab = crc64Table();
    }

    $crc = 0;

    for ($i = 0; $i < strlen($string); $i++) {
        $crc = $crc64tab[($crc ^ ord($string[$i])) & 0xff] ^ (($crc >> 8) & ~(0xff << 56));
    }

    return sprintf($format, $crc);
}

[#3] Clifford dot ct at gmail dot com [2012-08-07 08:54:38]

The crc32() function can return a signed integer in certain environments. Assuming that it will always return an unsigned integer is not portable.

Depending on your desired behavior, you should probably use sprintf() on the result or the generic hash() instead. Also note that integer arithmetic operators do not have the precision to work correctly with the integer output.

[#4] alban dot lopez+php [ at ] gmail dot com [2011-11-26 18:02:42]

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; } ?>

[#5] arris at zsolttech dot com [2011-10-19 05:17:00]

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

(use gmp module)

<?php define('POLY64REV', "d800000000000000"); define('INITIALCRC', "0000000000000000"); define('TABLELEN', 256); // 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)){ $part = gmp_xor(gmp_div_q($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!!!"); } ?>

[#6] sukitsupaluk at hotmail dot com [2011-09-08 03:04:25]

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); ?>

[#7] chernyshevsky at hotmail dot com [2010-09-22 15:54:08]

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.

[#8] gabri dot ns at gmail dot com [2010-09-15 22:05:28]

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)

[#9] jian at theorchard dot com [2010-02-17 10:13:28]

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.

[#10] berna (at) gensis (dot) com (dot) br [2009-09-29 20:16:09]

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); } ?>

[#11] dave at jufer dot info [2007-12-03 14:15:27]

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; } ?>

[#12] Ren [2007-10-03 11:53:47]

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)

[#13] slimshady451 [2007-06-20 02:14:58]

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.

[#14] mail at tristansmis dot nl [2007-05-30 01:36:32]

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; } ?>

[#15] roberto at spadim dot com dot br [2006-04-07 21:52:04]

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)); } ?>

[#16] Bulk at bulksplace dot com [2005-08-27 05:46:12]

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.

[#17] waldomonster at netjukebox dot demon dot nl [2004-04-23 08:48:52]

<?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

[#18] arachnid at notdot dot net [2004-04-13 20:44:12]

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.

[#19] same [2004-02-01 17:27:27]

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); ?>

[#20] quix at free dot fr [2003-05-05 13:19:18]

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; } ?>

[#21] spectrumizer at cycos dot net [2002-12-29 15:30:51]

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