PHP如何将gb2312网页内的中文转换成utf-8

function   gb2utf8($gb)         /*   Program   writen   by   sadly       modified   by   agun   */ 
{ 
if(!trim($gb)) 
return   $gb; 
$filename= "gb2312.txt"; 
$tmp=file($filename); 
$codetable=array(); 
while(list($key,$value)=each($tmp)) 
$codetable[hexdec(substr($value,0,6))]=substr($value,7,6); 

$ret= " "; 
$utf8= " "; 
while($gb) 
{ 
if   (ord(substr($gb,0,1))> 127) 
{ 
$this1=substr($gb,0,2); 
$gb=substr($gb,2,strlen($gb)); 
$utf8=u2utf8(hexdec($codetable[hexdec(bin2hex($this1))-0x8080])); 
for($i=0;$i <strlen($utf8);$i+=3) 
$ret.=chr(substr($utf8,$i,3)); 
} 
else 
{ 
$ret.=substr($gb,0,1); 
$gb=substr($gb,1,strlen($gb)); 
} 
} 
return   $ret; 
}