C++ to Delphi CheckSum code
 

typedef struct iphdr
{
u_char ip_hl:4, /* header length */
ip_v:4; /* version */
u_char ip_tos; /* type of service */
short ip_len; /* total length */
u_short ip_id; /* identification */
short ip_off; /* fragment offset field */
#define IP_DF 0x4000 /* dont fragment flag */
#define IP_MF 0x2000 /* more fragments flag */
u_char ip_ttl; /* time to live */
u_char ip_p; /* protocol */
u_short ip_sum; /* checksum */
struct in_addr ip_src,ip_dst; /* source and dest address */
} iphdr, *iphdr_ptr;


VOID RecalculateIPChecksum (
iphdr_ptr pIpHeader
)
{
unsigned short word16;
unsigned int sum = 0;
unsigned int i = 0;
PUCHAR buff;

// Initialize checksum to zero
pIpHeader->ip_sum = 0;
buff = (PUCHAR)pIpHeader;

// Calculate IP header checksum
for (i = 0; i < pIpHeader->ip_hl*sizeof(DWORD); i=i+2)
{
word16 = ((buff[i]<<8)&0xFF00)+(buff[i+1]&0xFF);
sum = sum+word16;
}

// keep only the last 16 bits of the 32 bit calculated sum and add the carries
while (sum>>16)
sum = (sum & 0xFFFF)+(sum >> 16);

// Take the one's complement of sum
sum = ~sum;

pIpHeader->ip_sum = htons((unsigned short) sum);
}

Re: C++ to Delphi CheckSum code
 

That C code is a mess. And it is dangerous because it uses bitfields (which C++ does not guarantee to be packed in any specific order -- so results vary by compiler!).

Alas, why don't programmers stp usng stpd shrt nonsns nms.

Anyway:

uses

  SysUtils,  // for PByteArray

  Winsock;   // for htons()



const

  IP_DF = $4000;  // don't fragment flag

  IP_MF = $2000;  // more fragments flag



type

  in_addr = record ... end;  // you must fill this in



  iphdr_ptr = ^iphdr;

  iphdr = packed record

    ip_hl__ip_v: byte;      // header length, version: four bits each

    ip_tos:      byte;      // type of service

    ip_len:      shortint;  // total length

    ip_id:       word;      // identification

    ip_off:      shortint;  // fragment offset field

    ip_ttl:      byte;      // time to live

    ip_p:        byte;      // protocol

    ip_sum:      word;      // checksum

    ip_src:      in_addr;   // source address

    ip_dst:      in_addr    // destination address

    end;



procedure RecalculateIPChecksum( pIpHeader: iphdr_ptr );

  var

    sum:    longword;

    i:      longword;

    buff:   PByteArray;  // see note 1

  begin

  sum := 0;

  i   := 0;



  // Initialize checksum to zero

  pIpHeader^.ip_sum := 0;

  buff := pIpHeader;



  // Calculate IP header checksum

  while i < (pIpHeader^.ip_hl__ip_v and $F) *sizeof( longword ) do  // see note 2

    begin

    inc( sum, (buff[ i ] shl 8) +buff[ i +1 ] );

    inc( i, 2 )

    end;



  // Keep only the last 16 bits of the 32 bit calculated sum and add the carries

  while (sum shr 16) <> 0 do

    sum := (sum and $FFFF) +(sum shr 16);



  // Take the one's complement of sum

  sum := sum xor $FFFFFFFF;



  // ...and store it in network order

  pIpHeader^.ip_sum := htons( sum )

  end;

The above code presumes the following:

1. typedef unsigned char* PUCHAR;
2. bitfields are packed in MS VC++ order [1], meaning that ip_hl is in the lower four bits and ip_v is in the upper four bits. If this is not the case you will need to change that and $F to shr 4.

Enjoy!

Re: C++ to Delphi CheckSum code
 

Thank you so much. This gives me a lot of help with other peaces of code.

Ray