Hướng dẫn dùng crc hash trong PHP

Ví dụ và cách sử dụng hàm crc32 trong PHP để tính CRC có độ dài 32-bit của một chuỗi.

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Miêu tả hàm crc32
Giá trị trả về
Description
Return Values

in Hàm xử lý chuỗi trong PHP

(PHP 4 >= 4.0.1, PHP 5)
crc32 – Tính CRC 32-bit của một chuỗi

Miêu tả hàm crc32

CRC32 (cyclic redundancy check 32-bit) là một loại hàm băm, được dùng để sinh ra giá trị kiểm thử có độ dài 32-bit của một chuỗi. Hàm này thông thường được dùng để xác nhận tính toàn vẹn của dữ liệu được truyền đi.

Cảnh báo: Kiểu số nguyên của PHP trên nền tảng 32-bit có thể dẫn đến kết quả là số nguyên âm khi sử dụng hàm crc32. Trên nền tảng 64bit hàm crc32() sẽ cho kết quả là số nguyên dương.

Vì vậy bạn cần sử dụng định dạng “%u” khi dùng hàm sprintf() hoặc printf() để in ra kết quả crc32() là dương và có định dạng thập phân.

Để hiển thị kết quả dưới dạng thập lục phân (hệ 16) bạn có thể sử dụng định dạng “%x” khi dùng hàm sprintf() hoặc printf() nhưng cũng có thể dùng hàm dechex(), cả 2 cách đều có tác dụng hiển thị kết quả của hàm crc32() thành số nguyên dương.

Trên nền tảng 64bit cũng có thể trả lại kết quả là số nguyên âm với các giá trị kết quả cao, phá vỡ quá trình chuyển đổi sang hệ 16 với phần âm thêm hậu tố 0xFFFFFFFF########. Với hệ 16 dường như hầu hết các trường hợp phổ biến nhất chúng tôi quyết định không phá vỡ quy trình này ngay cả khi nó phá vỡ phép so sánh nhị phân trực tiếp trong khoảng 50% số trường hợp khi chuyển từ 32 sang 64bits. Trong quá khứ, hàm trả về một số nguyên có thể không phải là ý tưởng tốt nhất và việc trả về một chuỗi hệ 6 (hex) ngay lập tức (ví dụ hàm md5()) sẽ có thể là một ý tưởng tốt hơn. Với một giải pháp linh động hơn bạn cũng có thể xem tới hàm hash(). hash(“crc32b”, $str) sẽ trả về chuỗi tương tự như dechex(crc32($str)).

Tham số

string

Dữ liệu cần tính.

Giá trị trả về

Trả về chuỗi kiểm tra crc32 là một số nguyên.

Ví dụ

Ví dụ 1 về hàm crc32()

Ví dụ dưới đây sẽ cho thấy cách in ra kết quả kiểm tra bằng hàm printf() :

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

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

//IN RA : 2191738434

(PHP 4 >= 4.0.1, PHP 5, PHP 7, PHP 8)

crc32 — Calculates the crc32 polynomial of a string

Description

crc32(string $string): int

Warning

Because PHP's integer type is signed many crc32 checksums will result in negative integers on 32bit platforms. On 64bit installations all crc32() results will be positive integers though.

So you need to use the "%u" formatter of sprintf() or printf() to get the string representation of the unsigned crc32() checksum in decimal format.

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", $str) will return the same string as str_pad(dechex(crc32($str)), 8, '0', STR_PAD_LEFT).

Parameters

string

The data.

Return Values

Returns the crc32 checksum of string as an integer.

Examples

Example #1 Displaying a crc32 checksum

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

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

`khash() -- maps a crc32 result into a (62-character) result`

";
print '';
var_dump($out);
print "\n\n\$GLOBALS['raw_crc32']:\n";
var_dump($GLOBALS['raw_crc32']);
print '
';
flush();
$pefile = __FILE__;
print "$pefile
";
ob_end_flush();
flush();
highlight_file($pefile);
print "
";
//-----------------------------------------------------------------------------------
/* CURRENT output
array(19) {
  [0]=>
  string(8) "4GFfc4: "
  [1]=>
  string(9) "76nO4L: 1"
  [2]=>
  string(8) "4GFfc4: "
  [3]=>
  string(9) "9aGcIp: 0"
  [4]=>
  string(9) "9aGcIp: 0"
  [5]=>
  string(9) "76nO4L: 1"
  [6]=>
  string(9) "76nO4L: 1"
  [7]=>
  string(9) "5b8iNn: 2"
  [8]=>
  string(9) "6HmfFN: 3"
  [9]=>
  string(10) "7ADPD7: ab"
  [10]=>
  string(11) "5F0aUq: abc"
  [11]=>
  string(12) "92kWw9: abcd"
  [12]=>
  string(13) "78hcpf: abcde"
  [13]=>
  string(16) "9eBVPB: abcdefoo"
  [14]=>
  string(17) "5TjOuZ: 248840027"
  [15]=>
  string(18) "5eNliI: 1365848013"
  [16]=>
  string(27) "4Q00e5: 9223372035488927794"
  [17]=>
  string(17) "6DUX8V: 901131979"
  [18]=>
  string(39) "5i2aOW: Sat, 13 Apr 2013 10:13:33 +0000"
}
*/
//-----------------------------------------------------------------------------------?>

i at morfi dot ru ¶

9 years ago

Implementation crc64() in php 64bit

/** * @return array */ 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;
}/**
 * @param string $string
 * @param string $format
 * @return mixed
 * 
 * Formats:
 *  crc64('php'); // afe4e823e7cef190
 *  crc64('php', '0x%x'); // 0xafe4e823e7cef190
 *  crc64('php', '0x%X'); // 0xAFE4E823E7CEF190
 *  crc64('php', '%d'); // -5772233581471534704 signed int
 *  crc64('php', '%u'); // 12674510492238016912 unsigned int
 */
function crc64($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);
}

Bulk at bulksplace dot com ¶

17 years ago

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.

Clifford dot ct at gmail dot com ¶

10 years ago

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.

slimshady451 ¶

15 years ago

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.

same ¶

18 years ago

bit by bit crc32 computation

dave at jufer dot info ¶

14 years ago

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

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

alban dot lopez+php [ at ] gmail dot com ¶

10 years ago

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

// 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 ¶

10 years ago

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

(use gmp module)

/* 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!!!");
}
?>

quix at free dot fr ¶

19 years ago

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:

$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(;;) {
            $i[email protected]fread($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 ¶

19 years ago

Here is a tested and working CRC16-Algorithm:

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 ¶

14 years ago

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)

arachnid at notdot dot net ¶

18 years ago

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.

sukitsupaluk at hotmail dot com ¶

11 years ago

small sample convert crc32 to character map

*/

?>

roberto at spadim dot com dot br ¶

16 years ago

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)); } ?>

chernyshevsky at hotmail dot com ¶

11 years ago

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:

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.

berna (at) gensis (dot) com (dot) br ¶

12 years ago

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

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:

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

mail at tristansmis dot nl ¶

15 years ago

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.

$crc

= abs(crc32($string));
   if( $crc & 0x80000000){
      $crc ^= 0xffffffff;
      $crc += 1;
   }/* Old solution
    * $crc = abs(crc32($string))
    */?>

toggio at writeme dot com ¶

6 years ago

A faster implementation of modbus CRC16

function crc16($data) { $crc = 0xFFFF; for ($i = 0; $i < strlen($data); $i++) { $crc ^=ord($data[$i]);

for ($j = 8; $j !=0; $j--) { if (($crc & 0x0001) !=0) { $crc >>= 1; $crc ^= 0xA001; } else $crc >>= 1; } } return $crc; }

gabri dot ns at gmail dot com ¶

11 years ago

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') 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;
}
?>

$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)

dotg at mail dot ru ¶

5 years ago

crc32() on php 32bit and 64 bit not equal in some values

i use abs for result in positive for 32 bit

not equal (crc32(1));?> 64 bit 2212294583 32 bit 2082672713

equal (crc32(3));?> 64 bit 1842515611 32 bit 1842515611

waldomonster at netjukebox dot demon dot nl ¶

18 years ago

$data = 'dot'; echo dechex(crc32($data)); ?> Returns 59278a3 Witch is missing a leading zero.

$data = 'dot'; echo str_pad(dechex(crc32($data)), 8, '0', STR_PAD_LEFT); ?> Returns the correct string: 059278a3

Hướng dẫn dùng crc hash trong PHP

Miêu tả hàm crc32

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Ví dụ 1 về hàm crc32()

Description

Parameters

Return Values

Examples

See Also

khash() -- maps a crc32 result into a (62-character) result

$pefile

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`khash() -- maps a crc32 result into a (62-character) result`