<?php

$ipArr    = explode('.','120.24.157.100');
$ip       = $ipArr[0] * 0x1000000
          + $ipArr[1] * 0x10000
          + $ipArr[2] * 0x100
          + $ipArr[3]
          ;


$ipVal = $ip;
$ipArr = array(0 =>floor($ipVal / 0x1000000) );
$ipVint   = $ipVal-($ipArr[0]*0x1000000); // for clarity
$ipArr[1] = ($ipVint & 0xFF0000)  >> 16;
$ipArr[2] = ($ipVint & 0xFF00  )  >> 8;
$ipArr[3] =  $ipVint & 0xFF;
$ipDotted = implode('.', $ipArr);

echo $ip, ' ', $ipDotted;

转载自：

• php.net