Golang tip of the day; PHP-compatible crc32

While porting (well, actually rewriting) an old PHP library to Go, I had to use a CRC (cyclic redundancy check) on a buffer. In old-school PHP, the standard is well established since PHP 4: just use crc32 from the strings package, and beware of the sign bit or, to be a bit more current while still compatible, use the hash() function from the hash package, like this example:

<?php    $hash = gmp_init(hash("crc32b", $url), 16);    $hex = gmp_strval($hash);?>

No big deal, Go has a crc32 package, so it should be a direct port, should it not ?

Trouble is, Go went a bit further than PHP (surprise, surprise), and documents its algorithms, unlike PHP just listing them at http://php.net/manual/en/function.hash-algos.php. To wit:

const (
        // IEEE is by far and away the most common CRC-32 polynomial.
        // Used by ethernet (IEEE 802.3), v.42, fddi, gzip, zip, png, ...
        IEEE = 0xedb88320

        // Castagnoli's polynomial, used in iSCSI.
        // Has better error detection characteristics than IEEE.
        // http://dx.doi.org/10.1109/26.231911
        Castagnoli = 0x82f63b78

        // Koopman's polynomial.
        // Also has better error detection characteristics than IEEE.
        // http://dx.doi.org/10.1109/DSN.2002.1028931
        Koopman = 0xeb31d82e
)

But PHP has no reference to the IEEE, Castagnoli, and Koopman polynomials, just listing crc and crc32. A quick check on values gives the expected equivalents.

Check with more values to ensure it was not just a collision, and we have a winner: PHP hash('crc32b', $value) is equivalent with Go crc32.ChecksumIEEE(value) . There had to be a reason why this was the only one of the three polynomials to be graced with a dedicated checkum method : neither Castagnoli nor Koopman have one.