Hash 函数
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PHP手册

hash_file

(PHP 5 >= 5.1.2, PECL hash >= 1.1)

hash_file — Generate a hash value using the contents of a given file

说明

string hash_file ( string $algo , string $filename [, bool $raw_output = false ] )

参数

algo

Name of selected hashing algorithm (i.e. "md5", "sha256", "haval160,4", etc..)

filename

URL describing location of file to be hashed; Supports fopen wrappers.

raw_output

When set to TRUE, outputs raw binary data. FALSE outputs lowercase hexits.

返回值

Returns a string containing the calculated message digest as lowercase hexits unless raw_output is set to true in which case the raw binary representation of the message digest is returned.

范例

Example #1 Using hash_file()

<?php
/* Create a file to calculate hash of */
file_put_contents('example.txt', 'The quick brown fox jumped over the lazy dog.');

echo hash_file('md5', 'example.txt');
?>

以上例程会输出：

5c6ffbdd40d9556b73a21e63c3e0e904

参见

Hash 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: Generate a hash value using the contents of a given file

用户评论:

apm at domain itsmee.co.uk (10-Jul-2011 12:56)

I have verified that the output of the "crc32" is the ITU I.363.5 algorithm (a.k.a. AAL5 CRC - popularised by BZIP2 but also used in ATM transmissions - the algorithm is the same as that in POSIX 1003.2-1992 in Cksum but that stuffs the size into the CRC at the end for extra measure).  However, the output is expressed in reverse order to many CRC programs.  Using the "standard" crctest.txt (numbers 1 to 9 in sequence - google it, it's not hard to find), php will output 181989fc - many other (Intel little endian) programs would output this as fc891918, hence the confusion (that I have had, at least).

The crc32b is the 32-bit Frame Check Sequence of ITU V.42 (used in Ethernet and popularised by PKZip).  The output from this CRC is popularised in Intel little endian format and would produce cbf43926 on the same file.

Anonymous (26-Apr-2011 05:55)

Please take note that hash-file will throw error on files >=2GB.

chernyshevsky at hotmail dot com (23-Sep-2010 12:01)

If you want to use hash_file() to get the CRC32 value of a file, use the following to unpack the hex string returned by the function to an integer (similar to crc32()):

$hash = hash_file('crc32b', $filepath);
$array = unpack('N', pack('H*', $hash));
$crc32 = $array[1];

gabri dot ns at gmail dot com (16-Sep-2010 04:58)

i've browsing about crc32 recently
from http://en.wikipedia.org/wiki/Cyclic_redundancy_check
#Commonly_used_and_standardized_CRCs
it is said that ethernet and png using the same polynomial, 0x04C11DB7

so, it still unclear (for me) wich standard does 'crc32' uses
IMO, 'crc32b' is the most common used in software
PKzip us this, 7zip and SVF file use this too

to check wether an implementation is using 'crc32b',
try to hash string or file containing string:
"123456789" (without quote of course :D )
it should return CBF43926

Keisial at gmail dot com (11-Sep-2008 07:46)

The 'octets reversed' you are seeing is the bug 45028 which has been fixed. http://bugs.php.net/bug.php?id=45028

The difference between crc32 and crc32b is explained on mhash man page. crc32 is the one used on ethernet, while crc32b is the one used on zip, png... They differ on the table used.

allaryin at gmail dot com (23-Jul-2008 11:16)

For those who are wondering, there appears to be no fundamental difference between hash_file('md5')/hash_file('sha1') and md5_file()/sha1_file(). They produce identical output and have comparable performance.

There is, however, a difference between hash_file('crc32') and something silly like crc32(file_get_contents()).

crc32(file_get_contents())'s results are most similar to those of hash_file('crc32b'), just with the octets reversed:

<?php
$fname = "something.png";

$hash = hash_file( 'crc32', $fname );
echo "crc32  = $hash\n";

$hash = hash_file( 'crc32b', $fname );
echo "crc32b = $hash\n";

$hash = sprintf("%x",crc32(file_get_contents($fname)));
echo "manual = $hash\n";
?>

crc32  = f41d7f4e
crc32b = 7dafbba4
manual = a4bbaf7d