zip文件，大小错误

Question

我有一个包含许多PDF文件的文件夹。我已经构建了一个脚本，将这些pdf文件分别压缩为100mb。

#!/usr/bin/php
<?php
$pathToFiles = "../pdffakturor_test/";
$maxFileSize = 100 * 1024 * 1024;
$counter = 1;
$currentsize = 0;
$created_at_datum = date("Ymd");
$created_at_clock = date("Hi");
$zip = new ZipArchive;

if($counter <= 10)
{
    $counter = sprintf("%02s", $counter);
}

$zip->open('PROD_SE_C_S_E_'.$created_at_datum.'_'.$created_at_clock.$counter.'.zip', ZipArchive::CREATE);
if ($handle = opendir($pathToFiles))
{
    while (false !== ($entry = readdir($handle)))
    {
        if (substr($entry, -4) == ".pdf")
        {
            $filesize = filesize($pathToFiles.$entry);

            if($currentsize >= $maxFileSize)
            {
                $zip->close();
                $zip = null;
                $zip = new ZipArchive;
                $currentsize = 0;

                if($counter <= 10)
                {
                    $counter = sprintf("%02s", $counter);
                }

                $zip->open('PROD_SE_C_S_E_'.$created_at_datum.'_'.$created_at_clock.$counter.'.zip', ZipArchive::CREATE);
                $counter++; 
            }
            $zip->addFile($pathToFiles.$entry, $entry);
            $currentsize += $filesize;
        }
    }
    closedir($handle);
}
?>

我遇到的问题是第一个拉链批次为183mb，其他为91,6mb。我无法弄清楚为什么第一个变成了183mb？