2楼说的不明白。去个列子最好

xiaodao35 发表于 2013-2-21 16:06
低4位保留，高4位移到R0为低4位，查表得到高4位，与原低4位相加！

可以帮忙写一段C语言代码么？
我对查表一直是一知半解……

unsigned char swap_xx(unsigned char x)
{
        unsigned char temp1 = x;//temp1 = 1011 0101
        unsigned char temp2 = 0;
        unsigned char temp3 = 0;
       
        temp2 = temp1 >> 4;// temp2 = 0000 1011
        for(unsigned char i = 0; i < 8 ;i++)
        {
                if(temp2 & 0x01)
                {
                        temp3 |= 0x01;
                }
                temp3 << = 1;
        }//temp3 = 1101 0000
        temp3 = (temp1&0x0f)|temp3;
        return temp3;
}

unsigned char ChanByte(unsigned char DatBye)
{
    unsigned char i, j = 0, k = 0, HightBit, LowBit;

        HightBit = DatBye & 0xf0;
        LowBit   = DatBye & 0x0f;

        for(i = 0; i < 4; i ++)
        {
            j = (HightBit >> (i + 4)) & 0x01;
                k |= j << (7 - i);
        }

        k |= LowBit;

        return k;
}