short unPack( unsigned char c )
{
    /* Only want lower four bit nibble */
    c = c & (unsigned char)0x0F ;

    if( c > 7 ) {
        /* Negative nibble */
        return( ( short )( c - 5 ) ) ;

    }
    else
    {
        /* positive nibble */
        return( ( short )c ) ;
    }
}