各位大哥帮忙看看本解释二进制函数的逆函数怎么写！！！

//解释二进制
function TForm_Main.hex3str(hexstr:string):string;
var
   onebyte:string;
   i,m:integer;
begin
   result:='';
   for i:=1 to length(hexstr) do
   begin
      onebyte:=copy(hexstr,1,1);
      delete(hexstr,1,1);
      for m:=0 to 255 do
      if chr(m)=onebyte then
      begin
         result:=result+inttohex(m,2);
         break;
      end;
   end;
end;
这函数的逆函数怎么写呢？