Поместить четыре числа от 1 до 4 в один байт

int a = 4;
int b = 2;
int c = 3;
int d = 4;

#include <iostream>
#include <cstring>
 
int compose(const int a, const int b, const int c, const int d)
{
  int returnValue = 0;
  char byteVal[sizeof(returnValue)] = {0};
  byteVal[0] = (char) a;
  byteVal[1] = (char) b;
  byteVal[2] = (char) c;
  byteVal[3] = (char) d;
  memcpy(&returnValue, &byteVal[0], sizeof(returnValue));
  return returnValue;
}
 
void decompose(const int src, int& a, int& b, int& c, int& d)
{
  char byteVal[sizeof(src)];
  memcpy(&byteVal[0], &src, sizeof(byteVal));
  a = byteVal[0];
  b = byteVal[1];
  c = byteVal[2];
  d = byteVal[3];
}
 
int main()
{
  int a = 4;
  int b = 3;
  int c = 1;
  int d = 4;
  std::cout<<"Values: a = "<<a<<", b = "<<b<<", c = "<<c<<", d = "<<d<<std::endl;
  int res = compose(a, b, c, d);
  std::cout<<"Composed value: "<<res<<std::endl;
  a = 0;
  b = 0;
  c = 0;
  d = 0;
  decompose(res, a, b, c, d);
  std::cout<<"Decomposed: a = "<<a<<", b = "<<b<<", c = "<<c<<", d = "<<d<<std::endl;
  return 0;
}

#include <iostream>
int main(int argc, char* argv[]) {
    int a = 4;
    int b = 2;
    int c = 3;
    int d = 1;
    char bitfield = (a & 0x03) + ((b << 2) & 0x0C) + ((c << 4) & 0x30) + ((d << 6) & 0xC0);
 
    std::cout << "a = " <<  ((bitfield & 0x03)?(bitfield & 0x03): 0x04)  << std::endl;
    std::cout << "b = " <<  (((bitfield & 0x0C) >> 2)?((bitfield & 0x0C) >> 2): 0x04) << std::endl;
    std::cout << "c = " <<  (((bitfield & 0x30) >> 4)?((bitfield & 0x30) >> 4): 0x04) << std::endl;
    std::cout << "d = " <<  (((bitfield & 0xC0) >> 6)?((bitfield & 0xC0) >> 6): 0x04) << std::endl;
 
    return 0;
}

sum=(a-1)+(b-1)*4+(c-1)*16+(d-1)*64;
...
a=sum%4+1;
b=(sum/4)%4+1;
c=(sum/16)%4+1;
d=sum/64+1;