PHP File Splitter (straight)

<?php
ini_set('memory_limit', '-1');
ini_set('max_execution_time', 30000);

$sampleSQL = file_get_contents('sampleSQL.txt');
$past = 0;
$PIN = ');';
$PINlen = mb_strlen( $PIN );
$partSize = 0.2*1024*1024;//BYTES, 20MB
$len = mb_strlen($sampleSQL) / $partSize;
echo 'Total File: ' . floor($len);
echo '<br>';
echo 'Each File Size: ' . $partSize;
echo '<br>';
echo 'Each File Size(MB): ' . $partSize/(1024*1024);
for($i=1; $i < $len; $i++){
	
	$splitpos = mb_strpos($sampleSQL, $PIN, $i * $partSize);
	if( $i == floor($len) ){
		$part = mb_substr($sampleSQL, $past + $PINlen );
	}else{
		if($i != 1){ $marginS = $PINlen; $marginE = 0; }else{  $marginS = 0; $marginE = $PINlen; }
		$part = mb_substr($sampleSQL, $past + $marginS, $splitpos-$past + $marginE );
	}
	
	$past = $splitpos;//get previous last as current start offset
	file_put_contents($i, $part);

}

?>