#include <iostream>
#include <vector>


int crc_check(std::vector<int> bitseq)
  //int crc_check(unsigned int *frame_plus_fcs,int nbits)
  //   Returns zero if there are no bit errors in the frame.
  //   The input is an array of nbits bits that includes the data
  //   frame followed by the Frame Check Sequence (FCS).  The array
  //   of bits is divided by the polynomial x^11 + x^9 + 1 (i.e. the
  //   bit pattern 101000000001).  If the result is zero, then there
  //   are no errors in the frame.  The frame should be a sequence of
  //   11-bit words.
{
  int reg[11];
  for (int ibit=0; ibit<11; ibit++) reg[ibit] = 0;
  
  std::vector<int>::iterator iter;

  for (iter = bitseq.begin(); iter != bitseq.end(); iter++) {
    int carry = reg[10];
    reg[10] = reg[9];
    reg[9]  = carry^reg[8]; // Exclusive OR
    reg[8]  = reg[7];
    reg[7]  = reg[6];
    reg[6]  = reg[5];
    reg[5]  = reg[4];
    reg[4]  = reg[3];
    reg[3]  = reg[2];
    reg[2]  = reg[1];
    reg[1]  = reg[0];
    reg[0]  = carry^(*iter); // Exclusive OR
  }
  
  int sum = 0;
  for (ibit=0; ibit<11; ibit++) sum += reg[ibit];
  
  std::cout << "sum:" << sum << endl;

  return sum;

}