#include <stdio.h>
#include <gmp.h>
#define GODFREY 0
#if GODFREY
  #define CHECK_BIT(var,pos) (((var) & (pos)) ? 2LL : -2LL)
  #define CHECK_BIT_G(var,pos) (((var) & (pos)) ? 1LL : -1LL)
#else
  #define CHECK_BIT(var,pos) (((var) & (pos)) ? 1LL : 0LL)
#endif
#define n 9
#define NPOS (2*n)

mpz_t bigsum;
mpz_t tmp;
long long int prod[n];
unsigned int k, j;
unsigned long long int sum, swp;

inline void updatesum(unsigned int odd)
{
    mpz_set_si(tmp,1);
    for(k=0; k < n; k++)
    {
      if(prod[k] == 0LL) 
      {
	return;
      }
      mpz_mul_si(tmp,tmp,prod[k]);
    }
    if(odd) mpz_sub(bigsum,bigsum,tmp);
    else mpz_add(bigsum,bigsum,tmp);
}

inline void calc(unsigned long long int gray)
{
  for (k=1; k <= n; k++)
  {
    sum = 0;
    swp = 1LL;
    for(j=1; j <= (NPOS-k); j++, swp<<=1) // n^2 calc of sum
      #if GODFREY
	sum += CHECK_BIT_G(gray,swp)*CHECK_BIT_G(gray,swp<<k);
      #else
	if(gray & swp) sum += CHECK_BIT(gray,swp<<k);
      #endif
    prod[k-1] = sum;
  }
}

int main(int argc, char *argv[])
{
  unsigned long long int x,min;
  unsigned long long int gray = 0;
  unsigned long long int bigN = (1LL<<(NPOS));
  unsigned int multiproc= 0; // are we running as one of several processes?
  unsigned int num_proc= 0; // log_2 of number of processes
  unsigned int proc_id= 0; // id of this proces. Range 0 .. 2^num_proc - 1
  mpz_init(bigsum);
  mpz_init(tmp);

  long long int hook= -1LL;
  int arg = 1; 
  while(arg<argc && *argv[arg]=='-') 
  { 
    switch(*(argv[arg]+1))
    { 
      case 'p': // multiproc - does _not_ work with -h and -r
	++arg;
	multiproc= 1;
	if (sscanf(argv[arg], "%d/%d", &proc_id, &num_proc) != 2) return -1;
	break;
      case 'h': // hooked
	++arg;
	hook= (1LL << ((2*n)-1));
	break;
      case 'r': // Rosa
	++arg;
	hook= (1LL << ((n+1)-1));
	break;
      default:
	return -1;
    }
    ++arg;
  }
  unsigned long long int length= bigN>>num_proc;
  unsigned long long int start= proc_id*length;
  unsigned long long int stop= start + length;
  gray = start^(start>>1LL);
  for (k=0; k < n; k++) prod[k] = 0LL;
  calc(gray);
  if(proc_id!=0)
    start++;
  for(x=start; x < stop; ++x)
  {
    min = x & (-x); // bit changed in graycode
    if (min>=hook) min<<=1; // fool the grey code to step over the hook
    gray ^= min; // graycode

    if(min&gray) // +1
    {

      swp=min>>1;
      for (k=0; k < n && swp; k++, swp>>=1)
      {
	prod[k] += CHECK_BIT(gray,swp);
      }

      swp=min<<1;
      for (k=0; k < n && swp < bigN; k++, swp<<=1)
      {
	prod[k] += CHECK_BIT(gray,swp);
      }
    }
    else // 0
    {
      swp=min>>1;
      for (k=0; k < n && swp; k++, swp>>=1)
      {
	prod[k] -= CHECK_BIT(gray,swp);
      }

      swp=min<<1;
      for (k=0; k < n && swp < bigN; k++, swp<<=1)
      {
	prod[k] -= CHECK_BIT(gray,swp);
      }
    }
    updatesum(x&1);
  }
  #if GODFREY
    gmp_printf("bigSum %Zd\n", bigsum);
    mpz_fdiv_q_2exp(bigsum, bigsum, NPOS);
  #endif
  if(hook>1) printf("hooked ");
  gmp_printf("skolem sequences of order %d: %Zd\n",n, bigsum);
}