Problème de traduction d'un Checksum Perl en langage C++

#include <stdio.h>
#include <math.h>

typedef unsigned int CRC;

CRC crc_16(unsigned char c);

CRC crc_16(unsigned char c)
{
   int i,j,k;

   for(i=0;i!=8;c>>=1,i++)
   {
        j = CRC+CRC;
	k = pow(2,16);
     	j = CRC%k;
      	
	CRC = j;

   }
   return CRC;
}

#!/usr/bin/perl -w

sub checksum16 ($) {
# calculates the checksum 16 of the given string argument
	my @bytes = unpack("C*", $_[0]);
	my $sum = 0;
	foreach(@bytes) {
		$sum += $_;
		$sum %= 2**16;
	}
	return $sum;
}
print checksum16 ("t");
print "\n";

#include <stdio.h>
#include <math.h>
#include <string.h>

typedef const char CRC;

CRC crc_16(unsigned char c)
{
   int i,j,k = 0;

   for(i=0;i!=8;c>>=1,i++)
   {
        k += c;
	k %= 1<<16;
   }
   return k;
}

int main()
{
printf("%u",crc_16('t'));
printf ("\n");
return 0;
}

#!/usr/bin/perl -w

sub checksum16 ($) {
# calculates the checksum 16
# of the given string argument
    my @bytes = unpack("C*", $_[0]);
    my $sum = 0;
    foreach(@bytes) {
	$sum += $_;
	$sum %= 2**16;
    }
    return $sum;
}
print checksum16 ("toto");
print "\n";

#include <stdio.h>

unsigned int crc_16(char* s)
{
  unsigned int sum = 0;
  while (s && *s)
  {
    sum += *s;
    sum %= 2 << 15;
    ++s;
  }

  return sum;
}

int main(void)
{
  printf("%u\n", crc_16("toto"));

  return 0;
}

#include <cstdlib>
#include <cstdio>
#include <string>

typedef const char CRC;

CRC crc_16( char c)
{
   int i,j,k = 0;

   for(i=0;i<sizeof(c);i++)
   {
	
        k += c;
	k %= 2<<16;
	c>>=1;
   }
   return k;
}

int main()
{
printf("%d",crc_16('t'));
printf ("\n");
return 0;
}

#include <iostream>

unsigned int crc_16(const std::string& s)
{
  unsigned int sum = 0;
  const unsigned int size = s.size();
  for (unsigned int i = 0; i < size; ++i)
  {
    sum += s[i];
    sum %= 2 << 15;
  }

  return sum;
}

int main()
{
  std::cout << crc_16("toto") << std::endl;

  return 0;
}