hash

<?php
class Test
{
    public const virtualHostNode = 100;

    public const HOST_MAP = [
        "http://img1.baidu.com",
        "http://img2.baidu.com",
        "http://img3.baidu.com",
        "http://img4.baidu.com",
        "http://img5.baidu.com",
    ];

    public static $servers = null;

    public static function getHashModId(string $val)
    {
        $res = sprintf("%u", crc32(md5($val)));
        return $res % 4294967295;
    }

    public static function getServers()
    {
        $result = [];
        foreach (self::HOST_MAP as $url) {
            for ($i = 1; $i <= self::virtualHostNode; $i++) {
                $result[self::getHashModId("{$url}_{$i}")] = $url;
            }
        }
        ksort($result);

        self::$servers = $result;
    }

    public static function getServer(string $key)
    {
        $servers = self::$servers;
        if (empty($servers)) {
            return;
        }

        $hashMod = self::getHashModId($key);
        $nowUrl = '';
        foreach ($servers as $id => $url) {
            if ($hashMod <= $id) {
                $nowUrl = $url;
                break;
            }
        }

        if (empty($nowUrl)) {
            $nowUrl = current($servers);
        }

        return $nowUrl;
    }
}

$tt = new Test();
$servers = $tt->getServers();

$weight = [];
for ($i = 1; $i <= 1000000; $i++) {
    $fileName = "test00{$i}.jpg";
    $url = $tt->getServer($fileName);
    $weight[] = $url;
}

$total = count($weight);
$arrayCount = array_count_values($weight);
foreach ($arrayCount as $url => $num) {
    $p = bcmul(bcdiv($num, $total, 6), 100, 2);
    echo "{$url}占比:{$p}%
";
}