ASP中只有UrlEncode，没有Urldecode问题的解决方法？

function urldecode(enstr)          'url解碼函數 
 dim destr 
 dim c,i,v 
 destr="" 
 for i=1 to len(enstr) 
   c=mid(enstr,i,1) 
   if c="%" then 
     v=eval("&h"+mid(enstr,i+1,2)) 
     if v<128 then 
       destr=destr&chr(v) 
       i=i+2 
     else 
       if isvalidhex(mid(enstr,i,3)) then 
         if isvalidhex(mid(enstr,i+3,3)) then 
           v=eval("&h"+mid(enstr,i+1,2)+mid(enstr,i+4,2)) 
           destr=destr&chr(v) 
           i=i+5 
         else 
           v=eval("&h"+mid(enstr,i+1,2)+cstr(hex(asc(mid(enstr,i+3,1))))) 
           destr=destr&chr(v) 
           i=i+3 
         end if 
       else 
         destr=destr&c 
       end if 
     end if 
   else 
     if c="+" then 
       destr=destr&" " 
     else 
       destr=destr&c 
     end if 
   end if 
 next 
 urldecode=destr 
end function 
 
function isvalidhex(str) 
 isvalidhex=true 
 str=ucase(str) 
 if len(str)<>3 then isvalidhex=false:exit function 
 if left(str,1)<>"%" then isvalidhex=false:exit function 
 c=mid(str,2,1) 
 if not (((c>="0") and (c<="9")) or ((c>="a") and (c<="z"))) then isvalidhex=false:exit function 
 c=mid(str,3,1) 
 if not (((c>="0") and (c<="9")) or ((c>="a") and (c<="z"))) then isvalidhex=false:exit function 
end function