问如何计算压缩包的Adler32校验和？

EN

define('MOD_ADLER', 65521);

function adler32($data) {
    $a = 1; $b = 0; $len = strlen($data);
    for ($index = 0; $index < $len; ++$index) {
        $a = ($a + $data[$index]) % MOD_ADLER;
        $b = ($b + $a) % MOD_ADLER;
    }
    return ($b << 16) | $a;
}

pack('H*', $checksum);

$dataStr = "abc";
$crcStr = hash('adler32', $dataStr);

<?php

error_reporting(E_ALL);

function hash_adler32_wrapper($data) {
    $digHexStr = hash("adler32", $data);

    // If version is better than 5.2.11 no further action necessary
    if (version_compare(PHP_VERSION, '5.2.11', '>=')) {
        return $digHexStr;
    }

    // Workaround #48284 by swapping byte order
    $boFixed = array();
    $boFixed[0] = $digHexStr[6];
    $boFixed[1] = $digHexStr[7];
    $boFixed[2] = $digHexStr[4];
    $boFixed[3] = $digHexStr[5];
    $boFixed[4] = $digHexStr[2];
    $boFixed[5] = $digHexStr[3];
    $boFixed[6] = $digHexStr[0];
    $boFixed[7] = $digHexStr[1];

    return implode("", $boFixed);
}

// Test fixture, plus expected output generated using the adler32 from zlib
$data_in = "abc";
$expected_out = 0x024d0127;

// PHP's hash function returns a hex hash value as a string so hexdec used to
// convert to number
$hash_out = hexdec(hash("adler32", $data_in));

// Get value via the wrapper function
$wrapper_out = hexdec(hash_adler32_wrapper($data_in));

printf("data_in:          %s\n", $data_in);
printf("expected_out:     0x%08x\n", $expected_out);
printf("builtin hash out: 0x%08x, %s\n", $hash_out,
        ($hash_out == $expected_out)? "OK" : "NOT OK");
printf("wrapper func out: 0x%08x, %s\n", $wrapper_out,
        ($wrapper_out == $expected_out)? "OK" : "NOT OK");

?>

function adler32($data) {
    $a = 1; $b = 0; $len = strlen($data);
    for ($index = 0; $index < $len; ++$index) {
        $a = ($a + ord($data[$index])) % 65521;
        $b = ($b + $a) % 65521;
    }
    return ($b << 16) | $a;
}