异或操作C++/组装

这是一个执行异或操作的代码。代码的作用类似于 x.bits.b = x.bits.c ^ x.bits.a我想要的是：x.bits.c = x.bits.a ^ x.bits.b

我试图将所有"cl"值更改为"bl"，但没有奏效。

#include "stdafx.h"
int main()
{
typedef union {
    unsigned char BYTE;
    struct {
        unsigned char a : 1;
        unsigned char b : 3;
        unsigned char c : 4;
    }bits;
}un_X;
un_X x;
x.BYTE = 0xFE;
x.bits.a = 1;
x.bits.b = 0;
x.bits.c = 2;

printf("n");
printf("BYTE = %Xn", x.BYTE);
printf("   a = %dn", x.bits.a);
printf("   b = %dn", x.bits.b);
printf("   c = %dn", x.bits.c);

_asm {
    //unsigned char a = x.BYTE & 0x01;
    mov al, x.BYTE
    and al, 0x01
    // unsigned char c = (x.BYTE & 0xF0) >> 4;
    mov cl, x.BYTE
    and cl, 0xF0
    shr cl, 4
    //unsigned char b = c ^ a;
    xor al, cl
    // x.BYTE &= 0xF1; // 1111 0001
    mov dl, x.BYTE
    and dl, 0xF1
    // x.BYTE |= (b << 1);
    shl al, 1
    or dl, al
    mov x.BYTE, dl
}


printf("n");
printf("BYTE = %Xn", x.BYTE);
printf("   a = %dn", x.bits.a);
printf("   b = %dn", x.bits.b);
printf("   c = %dn", x.bits.c);
getchar();
return 0;
}

我希望 a 和 b 是常数，c 是可变的。