crc32

(PHP 4 >= 4.0.1, PHP 5)

crc32 -- 计算一个字符串的 crc32 多项式

描述

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()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:

例子 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()sha1()


add a note add a note User Contributed Notes
angelo [at] mandato {period} com
30-Oct-2006 06:25
If you are trying to decide on a function for file verification, I came to the conclusion that md5_file() is the best all around solution.

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.
Tim
22-Aug-2006 01:26
What "info at b1g dot de" wrote about MD5 is not completely correct. He wrote:

"MD5 (32Byte) is more precise then CRC32 (4Byte)"

It is correct that MD5 is "more precise" than CRC32, but it does not contain 32 bytes, but 16 bytes. (SHA-1: 20 bytes)

Apart from that one cannot compare MD5 to CRC32 just by comparing its number of bits. The underlying algorithm is more important.

-Tim
roberto at spadim dot com dot br
08-Apr-2006 12:52
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));
}
administrador(ensaimada)sphoera(punt)com
17-Mar-2006 07:42
To obtain the adler32 hash from a string, you can use this simple function:
<?php
 
function adler32($buf){
  
$low = 1;
  
$high = 0;
  
$len = strlen($buf);
   for (
$n = 0; $n < $len; $n++) {
      
$low =  ($low + ord($buf[$n])) % 65521;
      
$high = ($high + $low) % 65521;
   }
  
$crc = $high * 65536 + $low;
   return
$crc;
 }
 
// and for entire files:
 
function file_adler32($filename){
     return
adler32(file_get_contents($filename));
 }
?>

more functions at http://www.sphoera.com/
info at b1g dot de
14-Feb-2006 11:12
I think nathanzadoks at yahoo dot co dot uk's function is not very good for checksums - it does not make any sense to build a md5 hash from a crc32 hash - MD5 (32Byte) is more precise then CRC32 (4Byte), so the MD5-encoding would not make sense. As PHP returns the MD5 hash in ASCII representation already, you do not need to base64-encode it, too. So a simple

md5($content)

or

sha1($content)

would be more precise and secure.
nathanzadoks at yahoo dot co dot uk
28-Jan-2006 02:54
If you want to make checksums use my checksum function
Usage: checksum($data);

<?php
function checksum($content){
   return
base64_encode(md5(crc32($content)));
}
?>
Sb.
26-Sep-2005 04:58
To have a 8 digits hexadecimal representation :

   $crc32 = sprintf('%08X', crc32($string)) ;
Bulk at bulksplace dot com
27-Aug-2005 08:46
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 04:26
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;
}

?>
Johan
13-May-2005 06:12
Here is a php version of the Java String hashCode:
( produced for: http://openmusic.op.funpic.org/catalog/ )

/**
 * Calculate hash code for a string computed as
 * s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
 * Equal to java.lang.String.hashCode()
 *
 * Returns an integer.
 */
function toID($link) {
   $link = (string)$link;
   $len = strLen($link);
   $sum = 0;
   for ($i = 0; $i < $len; $i++) {
       $sum = (int)(31 * $sum + getASCIICode($link[$i]));
       // echo($sum . "<br>");
   }

   return ((int)$sum);
}

// get char as int, - see example codes at intval on the subject.
function getASCIICode($caracter) {
// ...
}
gribber (_at) hellburner (dot_) net
19-May-2004 05:41
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
23-Apr-2004 11:48
<?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 11:44
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 09:27
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);

?>
sandeep_k_ghosh at hotmail dot com
16-Oct-2003 01:08
This function returns the unsigned crc32 value. I realized it's not very obvious from the current documentation.

<?php
/**
 * Function to compute the unsigned crc32 value.
 * PHP crc32 function returns int which is signed, so in order to get the correct crc32 value
 * we need to convert it to unsigned value.
 *
 * @param $str - String to compute the unsigned crc32 value.
 * @return $var - Unsinged inter value.
 */
function computeUnsignedCRC32($str){
  
sscanf(crc32($str), "%u", $var);
   return
$var;
}
?>
xethmir at yournextclient dot com
17-Jul-2003 10:12
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";
?>
sergi34 at megacceso dot com
10-Jun-2003 06:27
If you want to display a crc checksum correctly, you need to format it to unsigned because PHP int type is signed.

example:

<?php
$crc
= crc32("String where we calculate the checksum");
printf("%u", $crc);
?>
quix at free dot fr
06-May-2003 04:19
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 10:22
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 07:30
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