PHP 的 crc32、crc32b 以及 hash_file

PHP 上 CRC32 的資料時,查到讓人噴飯的 comment

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

不只是 hash_file() 抓出來不一樣,連 algorithm 都來亂...

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