scrambler.hh

COPE the first practical network coding scheme which is developped on click

#ifndef SCRAMBLER_HH
#define SCRAMBLER_HH

#include<click/packet.hh>

/*
 * note: not an element!

 * xor's two packets 
 */

CLICK_DECLS

class Scrambler { public:
  
  Scrambler()  {}		
  ~Scrambler() {}		
  
  inline WritablePacket* xor_packet(Packet *packet1, Packet *packet2, uint16_t, uint16_t);
};

// do we need 'inline'?
inline WritablePacket *
Scrambler::xor_packet(Packet *packet1, Packet *packet2, uint16_t len1, uint16_t len2)
{
  // note that packets should arrive without ethernet headers
  // not sure if the check is necessary
  if (!packet1 || !packet2)  // add a chatter?  click_chatter... #include <click/glue.hh> in that case 
    return 0;


//*** need to extract packet header first

// might need something like...
//  click_ether *eh = (click_ether *) p->data();
//  struct srpacket *pk = (struct srpacket *) (eh+1);

  WritablePacket *p_out;
  unsigned char *p_out_data;

  //int len1 = packet1->length(); 
  //int len2 = packet2->length();
//*** see if the length include any end of string symbol

  int i;

// *** need to make sure we don't encode IP headers, or actually...?

// the following could be optimised now that len1 and len2 are both passed to the function
// but we'll leave it for now

  // first check if the two packets are of equal length
  // pad up the shorter one with '0'
  // xor the data
  if (len1 < len2) {
    p_out = packet2->clone()->uniqueify();
    const unsigned char *p1_data = packet1->data();
    p_out_data = p_out->data();

    for (i = 0; i < len1; i++)      
      p_out_data[i] ^= p1_data[i];

    // xor the rest with a sequence of "0"
    for (; i < len2; i++)
      p_out_data[i] ^= char(0);  //*** is that right?!?!
  } else {
    p_out = packet1->clone()->uniqueify();
    const unsigned char *p2_data = packet2->data();
    p_out_data = p_out->data();

    for (i = 0; i < len2; i++)      
      p_out_data[i] ^= p2_data[i];

    // xor the rest with a sequence of "0"
    for (; i < len1; i++)
      p_out_data[i] ^= char(0);  //*** is that right?!?!
  }

  return p_out;
}

CLICK_ENDDECLS

#endif