php获取/dev/urandom随机数

// equiv to rand, mt_rand
// returns int in *closed* interval [$min,$max]
function devurandom_rand($min = 0, $max = 0x7FFFFFFF) {
    $diff = $max - $min;
    if ($diff < 0 || $diff > 0x7FFFFFFF) {
    throw new RuntimeException("Bad range");
    }
    $bytes = mcrypt_create_iv(4, MCRYPT_DEV_URANDOM);
    if ($bytes === false || strlen($bytes) != 4) {
        throw new RuntimeException("Unable to get 4 bytes");
    }
    $ary = unpack("Nint", $bytes);
    $val = $ary['int'] & 0x7FFFFFFF;   // 32-bit safe
    $fp = (float) $val / 2147483647.0; // convert to [0,1]
    return round($fp * $diff) + $min;
}      

function randomFromDev($len)
{
    $fp = @fopen('/dev/urandom','rb');
    $result = '';
    if ($fp !== FALSE) {
        $result .= @fread($fp, $len);
        @fclose($fp);
    }
    else
    {
        trigger_error('Can not open /dev/urandom.');
    }
    // convert from binary to string
    $result = base64_encode($result);
    // remove none url chars
    $result = strtr($result, '+/', '-_');
    // Remove = from the end
    $result = str_replace('=', ' ', $result);
    return $result;
}