#include<stdio.h>
typedef struct Divide8Bits_t
{
char firstHalf:4;
char secondHalf:4;
}Divide8Bits;
char FIL_historyTable = 0 ;
int main()
{
char wlgroup =1;
Divide8Bits *ptr = (Divide8Bits *)&FIL_historyTable;
if( !(wlgroup&0x1) )
ptr->firstHalf = 5; // example
else
ptr->secondHalf = 10; // example
}