如何高效把一字节的位对换, bit0和bit7,bit1和bit6,以此类推.

#include<stdio.h>

#include<stdlib.h>

//异或法

unsigned char byteReverse(unsigned char val) {



	int i;



	for (i = 0; i < 4; i++) {

		if (((val &(1 << i)) >> i) ^ ((val & (1 << (7 - i))) >> (7 - i)))

			val ^= (1 << i) | (1 << (7 - i));

	}

	return val;

}



//移位法：

unsigned char byteReverse1(unsigned char value) {

	unsigned char a = 0, b = 0, c = 0;

	for (int i=0;i<4;i++)

	{

		a = value&(0x80>>i);

		b = value&(0x01 << i);

		c = c + (b << (7 - 2 * i)) + (a >> (7 - 2 * i));

	}

	return c;

}





//如用C语言，“蝶形交换”最好

unsigned char byteReverse2(unsigned char a) {

	a = (a << 4) | (a >> 4);

	a = ((a << 2) & 0xcc) | ((a >> 2) & 0x33);

	a = ((a << 1) & 0xaa) | ((a >> 1) & 0x55);

	return a;

}



//蝶形交换，下面三句顺序随意

unsigned char byteReverse3(unsigned char a) {

	a = ((a << 4) & 0xf0) | ((a >> 4) & 0x0f);

	a = ((a << 2) & 0xcc) | ((a >> 2) & 0x33);

	a = ((a << 1) & 0xaa) | ((a >> 1) & 0x55);

	return a;

}





//还是觉得查表简单点：

unsigned char byteReverse4(unsigned char dat) {

	const unsigned char table[16] = { 0, 0x08, 0x04, 0x0c, 0x02, 0x0a, 0x06, 0x0e, 0x01, 0x09, 0x05, 0x0d, 0x03, 0x0b, 0x07, 0x0f };

	dat = table[(dat & 0xf0) >> 4] | (table[dat & 0x0f] << 4);

	return dat;

}



unsigned char byteReverse5(unsigned char data)

{

	unsigned char ret = 0;

	for (unsigned char i = 0; i< 8; i++)

	{

		ret <<= 1;

		if (data & 0x01)



		{

			++ret;

		}

		data >>= 1;

	}

	return ret;

}



unsigned char byteReverse6(unsigned char val)

{

	unsigned char  dat_b, i;

	dat_b = 0x00;

	for (i = 0; i <= 7; i++)

	{

		dat_b = dat_b | ((val >> i) & 0x01);

		if (i == 7)break;

		dat_b = dat_b << 1;

	}

	val = dat_b;

	return val;

}



void byteReverse7(unsigned char tar, unsigned char *pdata)

{

	unsigned char temp1 = (tar & 0x80) >> 7;

	unsigned char temp2 = (tar & 0x40) >> 5;

	unsigned char temp3 = (tar & 0x20) >> 3;

	unsigned char temp4 = (tar & 0x10) >> 1;

	unsigned char temp5 = (tar & 0x08) << 1;

	unsigned char temp6 = (tar & 0x04) << 3;

	unsigned char temp7 = (tar & 0x02) << 5;

	unsigned char temp8 = (tar & 0x01) << 7;

	*pdata = (temp1) | (temp2) | (temp3) | (temp4) | (temp5) | (temp6) | (temp7) | (temp8);

}



//有问题

const unsigned char jh_tab[8] = { 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80 };

unsigned char byteReverse8(unsigned char in_data)

{

	unsigned char i;

	unsigned char aa[8];

	unsigned char back_data = 0;

	for (i = 0; i< 8; i++)

	{

		aa[i] = in_data & jh_tab[i];

	}

	aa[0] = aa[0] << 7;

	aa[1] = aa[1] << 5;

	aa[2] = aa[2] << 3;

	aa[3] = aa[3] << 1;

	aa[7] = aa[7] >> 7;

	aa[6] = aa[6] >> 5;

	aa[5] = aa[5] >> 3;

	aa[4] = aa[4] >> 1;

	for (i = 0; i< 8; i++)

	{

		back_data = back_data + aa;

	}

	back_data = back_data;

	return back_data;

}





void byteReverse9()

{

	unsigned char  c = 0x20;

	unsigned char b = 0;

	char i;

	unsigned char P1 = c;

	unsigned char P2 = b;

	for (i = 0; i< 8; i++)

	{

		b <<= 1;

		b += c & 0x01;

		c >>= 1;

		P1 = c;

		P2 = b;

	}

	while (1);

}





void main()

{

	char data = 0x96;

	printf("@@@@@%x\n", byteReverse1(data));

}













 /*

 //汇编法

#ifndef_COMMON_H_

#define_COMMON_H_



#define__SWAP7_0(_short)\

(__extension__({                             \

    uint8_t __result =  (uint8_t)(_short);    \

    __asm__ __volatile__                    \

    (                                       \

        "mov__tmp_reg__,%0" "\n\t"       \

        "ldir25,8"          "\n\t"       \

        "L_%=:" "lsr__tmp_reg__"    "\n\t"       \

        "rol%0"             "\n\t"       \

        "decr25"            "\n\t"       \

        "brneL_%="           "\n\t"       \

        : "=r" (__result)                   \

        : "0"  (__result)                   \

                : "memory"                \

   );                                       \

    __result;                                \

}))



#defineSWAP7_0(_short)__SWAP7_0((uint8_t)(_short))

#endif



int main(void)

{

	  char i;

	  i =  0b01100111;

	  i =  SWAP7_0(i); 

	  PORTB = i;

}

*/