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Development Platform:
Delphi

IpHdr.pas：Code Content
							unit IpHdr;
interface
uses Windows,WinSock;
type
TIPHdr=record
    ip_verlen:BYTE;
    ip_tos:Byte;
    ip_totallength:Word;
    ip_id:Word;
    ip_offset:Word;
    ip_ttl:Byte;
    ip_protocol:Byte;
    ip_checksum:Word;
    ip_srcaddr:DWORD;
    ip_destaddr:DWORD;
    end;
PIPHdr=^TIPHdr;
TUDPHdr=record
    udp_srcport:Word;
    udp_destport:Word;
    udp_length:Word;
    udp_checksum:Word;
    end;
PUDPHdr=^TUDPHdr;
function inet_checksum(var buf;buflen:Integer):Word;
function LookupName(const name:string;var addr:TInAddr):Boolean;
implementation
function LookupName(const name: string;var addr:TInAddr):Boolean;
var
  HostEnt: PHostEnt;
begin
  Result:=False;
  addr.S_addr:=inet_addr(PChar(name));
  if(addr.S_addr=-1)then
  begin
    HostEnt := gethostbyname(PChar(Name));
    FillChar(Addr, SizeOf(Addr), 0);
    if HostEnt <> nil then
    begin
      with addr, HostEnt^ do
      begin
        S_un_b.s_b1 := h_addr^[0];
        S_un_b.s_b2 := h_addr^[1];
        S_un_b.s_b3 := h_addr^[2];
        S_un_b.s_b4 := h_addr^[3];
      end;
    Result:=True;
    end;
  end
  else Result:=True;
end;
function inet_checksum(var buf;buflen:Integer):Word;
var
pBuf:PWord;
cksum:DWORD;
begin
cksum:=0;
pBuf:=PWord(buf);
while(buflen>1)do
    begin
    cksum:=cksum+pBuf^;
    Inc(pBuf);
    Dec(buflen,SizeOf(Word));
    end;
if(buflen<>0)then
    begin
    cksum:=cksum+pBuf^;
    end;
cksum:=(cksum shr 16)+(cksum and $ffff);
cksum:=cksum shr 16;
result:=not cksum;
end;
//---------------------------------------------
//USHORT checksum(USHORT *buffer, int size)
//{
//    unsigned long cksum=0;
//
//    while (size > 1)
//    {
//        cksum += *buffer++;
//        size  -= sizeof(USHORT);
//    }
//    if (size)
//    {
//        cksum += *(UCHAR*)buffer;
//    }
//    cksum = (cksum >> 16) + (cksum & 0xffff);
//    cksum += (cksum >>16);
//
//    return (USHORT)(~cksum);
//}
//--------------------------------------------------
end.

						