位操作面試題

[jiazheng]

有一個32位的整數，要將基中的第0位，每31位交換，第1位與第30位交換，第2位與29位交換，以此類推。

[小清新爱大光明]

#include <iostream>
#include <bitset>
using namespace std;

int main()
{
	int a; 
	size_t low = 0, high = 31;

	cin>>a;

	bitset<32> bitvec(a);
	bitset<1> bitvec_temp;
	cout<<bitvec<<endl;

	while(low < high)
	{
		bitvec_temp[0] = bitvec[low];
		bitvec[low] = bitvec[high];
		bitvec[high] = bitvec_temp[0];
		++low;
		--high;
	}
	cout<<bitvec<<endl;

	return 0;
}

[wumuzi]

这个就是循环左移31位

[AIGPTchina]

#include "stdio.h"
#include <string.h>
typedef unsigned char BYTE;
typedef unsigned short WORD;
typedef unsigned int DWORD; /* 32 bit data type */

void shi2bin(DWORD val,BYTE *dest,DWORD len)
{
int mo=0,d=0;// 商、余
while(len>=0)
{
dest[len--]=val%2+'0';
d=val%2;
val=val/2;
mo=val;
if((d==1)&&(mo==0))break;
}

}

swap(BYTE data[])
{
BYTE temp;
for(int i=0,j=31;i<16,j>15;i++,j--)
{
temp=data[i];
data[i]=data[j];
data[j]=temp;
}
}




void main()
{
BYTE str[33];
memset(str,'0',32);
str[32]='\0';
shi2bin(405,str,31); // 十进制为:405
for(int i=0;i<32;i++)
printf("%c",str[i]);
printf("\n");
swap(str);
for(int j=0;j<32;j++)
printf("%c",str[j]);
}

[21011111111]

#include <iostream>
#include <cstdlib>
using namespace std;
const int bit = 32;
int r8(int n)
{
int halfbit = int(bit/2);
for(int i = 0; i < halfbit; ++i){
int tf = 1 << (bit - 1 - i);
int tb = 1 << i;
if(((n & tf) >> (bit - 1 - i)) == ((n & tb) >> i)){
continue;
}else{
n = n ^ tf;
n = n ^ tb;
}
}
return n;
}

int main(int argc, char** argv)
{
cout << argv[1] << endl;
cout << r8(atoi(argv[1])) << endl;
return 0;
}

[we_sky2008]

#include<stdio.h>
#include<stdlib.h>

typedef unsigned int u32;

//迭代法
unsigned reverse_val(u32 val)
{
    unsigned int low,  hig;
    
    for (low = 1, hig = 1 << ((sizeof(val) << 3) - 1); low < hig; low <<= 1, hig >>= 1)
    {
        if (((val & low) && !(val & hig)) || (!(val & low) && (val & hig)))
        {
            val ^= low;
            val ^= hig;
        }
    }
    
    return val;
}

int main()
{
    u32 val = 0x12345678;
    
    printf("%x\n", reverse_val(val));

    system("pause");
    return 0;
}

[we_sky2008]

#include<stdio.h>
#include<stdlib.h>

typedef unsigned int u32;

//单字节查表法
const unsigned char conv_tbl[256] =
{
    0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0,  /* 0x00 ... */
    0x10, 0x90, 0x50, 0xD0, 0x30, 0xB0, 0x70, 0xF0,
    0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8,  /* 0x10 ... */
    0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8,
    0x04, 0x84, 0x44, 0xC4, 0x24, 0xA4, 0x64, 0xE4,  /* 0x20 ... */
    0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4,
    0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC,  /* 0x30 ... */
    0x1C, 0x9C, 0x5C, 0xDC, 0x3C, 0xBC, 0x7C, 0xFC,
    0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2,  /* 0x40 ... */
    0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2,
    0x0A, 0x8A, 0x4A, 0xCA, 0x2A, 0xAA, 0x6A, 0xEA,  /* 0x50 ... */
    0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA,
    0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6,  /* 0x60 ... */
    0x16, 0x96, 0x56, 0xD6, 0x36, 0xB6, 0x76, 0xF6,
    0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE,  /* 0x70 ... */
    0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE,
    0x01, 0x81, 0x41, 0xC1, 0x21, 0xA1, 0x61, 0xE1,  /* 0x80 ... */
    0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1,
    0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9,  /* 0x90 ... */
    0x19, 0x99, 0x59, 0xD9, 0x39, 0xB9, 0x79, 0xF9,
    0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5,  /* 0xA0 ... */
    0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5,
    0x0D, 0x8D, 0x4D, 0xCD, 0x2D, 0xAD, 0x6D, 0xED,  /* 0xB0 ... */
    0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD,
    0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3,  /* 0xC0 ... */
    0x13, 0x93, 0x53, 0xD3, 0x33, 0xB3, 0x73, 0xF3,
    0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB,  /* 0xD0 ... */
    0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB,
    0x07, 0x87, 0x47, 0xC7, 0x27, 0xA7, 0x67, 0xE7,  /* 0xE0 ... */
    0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7,
    0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF,  /* 0xF0 ... */
    0x1F, 0x9F, 0x5F, 0xDF, 0x3F, 0xBF, 0x7F, 0xFF
};

unsigned reverse_val_table(u32 val)
{
    int i, j;
    unsigned char *p = (unsigned char *)&val;

    //先按byte翻转
    for (i = 0, j = sizeof(val) - 1; i < j; ++i, --j)
    {
        unsigned char tmp = p[i];
        p[i] = p[j];
        p[j] = tmp;
    }

    //再按bit翻转
    for (p = (unsigned char *)&val, i = 0; i < sizeof(val); ++i)
    {
        p[i] = conv_tbl[p[i]];
    }

    return val;
}

int main()
{
    u32 val = 0x12345678;

    printf("%x\n", reverse_val_table(val));
    
    system("pause");
    return 0;
}

[we_sky2008]

#include<stdio.h>
#include<stdlib.h>

typedef unsigned int u32;

//半字节查表法
const unsigned char conv_tbl_half_byte[16] = 
{
    0x00, 0x08, 0x04, 0x0c, 0x02, 0x0a, 0x06, 0x0e,
    0x01, 0x09, 0x05, 0x0d, 0x03, 0x0b, 0x07, 0x0f
};

unsigned reverse_val_halfbyte_table(u32 val)
{
    int i, j;
    unsigned char *p = (unsigned char *)&val;

    //先按byte翻转
    for (i = 0, j = sizeof(val) - 1; i < j; ++i, --j)
    {
        unsigned char tmp = p[i];
        p[i] = p[j];
        p[j] = tmp;
    }

    //再半字节翻转并交换翻转后的高低半字节
    for (i = 0; i < sizeof(val); ++i)
    {
        //将低四位翻转后移至高四位，将高四位翻转移至低四位，这样就达到了半字节翻转并交换翻转后的高低半字节
        p[i] = (conv_tbl_half_byte[p[i] & 0x0f] << 4) | (conv_tbl_half_byte[p[i] >> 4]);
    }

    return val;
}

int main()
{
    u32 val = 0x12345678;

    printf("%x\n", reverse_val_halfbyte_table(val));

    system("pause");
    return 0;
}