求一个网段的开始、结束IP地址

<?php
function mask2bin($n)
{
	$n = intval($n);
	if($n<0||$n>32) 
	die('error submask');
	return str_repeat("1", $n).str_repeat("0",32-$n);
}
function revBin($s)
{
	$p=array('0','1','2');
	$r=array('2','0','1');

	return str_replace($p,$r,$s);
}

function startIp($str,$bSub)
{
	$bIp = decbin($str);
	$bIp = str_pad($bIp,8,"0",STR_PAD_LEFT);
	$sIp = bindec($bIp & $bSub);
	return $sIp;
}
function endIp($str,$bSub)
{
	$bIp = decbin($str);
	$bIp = str_pad($bIp,8,"0",STR_PAD_LEFT);
	$eIp = bindec($bIp | revBin($bSub));
	return $eIp;
}

$ip = array('192','168','1','5');//设定IP地址，可以从表单获取，这里只作演示
$mask = '24';                    //设置掩码

$bSub = mask2bin($mask);         //将子网掩码转换二进制
$mask = array();
$mask[] = substr($bSub,"0",8);   //将子网掩码每8位分一段
$mask[] = substr($bSub,"8",8);
$mask[] = substr($bSub,"16",8);
$mask[] = substr($bSub,"24",8);

echo '<table summary="result" border="1" cellspacing="1" cellpadding="0" >
  <tbody>

    <td align="right" ><font size="2">掩码:</font></td>
    <td>
	<font size="2">';

for ($i=0;$i<4;$i++)
{
   echo bindec($mask[$i]);
   if($i!=3)
   echo ".";
}

echo '</font>
	</td>
	</tr>
  <tr>
    <td align="right"><font size="2">网络地址:</font></td>
    <td>
	<font size="2">';

	for ($i=0;$i<4;$i++)
    {
	  echo startIp($ip[$i],$mask[$i]);
	  if($i!=3)
	  echo ".";
    }

echo '</font> 
	</td>
	</tr>
		</td>
	</tr>
  <tr>
    <td align="right"><font size="2">第一个可用:</font></td>
    <td>
	<font size="2">';

	for ($i=0;$i<3;$i++)
    {	  
	  echo startIp($ip[$i],$mask[$i]);	  
	  echo ".";
    }
	$ip_4 = startIp($ip[3],$mask[3]);
	echo ++$ip_4;

	echo '</font> 
	</td>
	</tr>
  <tr>
    <td align="right"><font size="2">最后可用:</font></td>
    <td>
	<font size="2">';

	for ($i=0;$i<3;$i++)
    {
	  echo endIp($ip[$i],$mask[$i]);
	  echo ".";
    }
	$ip_4 = endIp($ip[3],$mask[3]);
	echo --$ip_4;
echo '
    </font>
	</td>
	</tr>
  <tr>
    <td align="right"><font size="2">广播地址:</font></td>
    <td>
	<font size="2">';

	for ($i=0;$i<4;$i++)
    {
	  echo endIp($ip[$i],$mask[$i]);
	  if($i!=3)
	  echo ".";
    }

?>