php求一个网段开始与结束IP地址的方法

<?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 ".";
  }
?>