1.判断奇偶
if (a & 1)
{
printf("%i is an odd number", a);
}
2.交换两数
void Swap(int &a, int &b)
{
if (a != b)
{
a ^= b;
b ^= a;
a ^= b;
}
}
3.变换符号
int SignReversal(int a)
{
return ~a + 1;
}
4.求绝对值
int my_abs(int a)
{
int i = a >> 31;
return ((a ^ i) - i);
}
注：如果 a 是负数，那么 a 右移 31 位为 -1
5.高低位交换
#include <stdio.h>
template <class T>
void PrintfBinary(T a)
{
int i;
for (i = sizeof(a) * 8 - 1; i >= 0; --i)
{
if ((a >> i) & 1)
putchar('1');
else
putchar('0');
if (i == 8)
putchar(' ');
}
putchar ('\n');
}
int main()
{
printf("Before: ");
unsighed short a = 12345;
PrintfBinary(a);
printf("After: ");
a = (a >> 8) | (a << 8);
PrintfBinary(a);
return 0;
}
6.二进制逆序
#include <stdio.h>
int main()
{
printf("Before: ");
unsigned short a = 12345;
PrintfBinary(a);
printf("After: ");
a = ((a & 0xAAAA) >> 1) | ((a & 0x5555) << 1);
a = ((a & 0xCCCC) >> 2) | ((a & 0x3333) << 2);
a = ((a & 0xF0F0) >> 4) | ((a & 0x0F0F) <<4);
a = ((a & 0xFF00) >> 8) | ((a & 0x00FF) <<8);
PrintfBinary(a);
return 0;
}
7.二进制中 1 的个数
#include <stdio.h>
int main()
{
unsigned short a = 12345;
a = ((a & 0xAAAA) >> 1) + (a & 0x5555);
a = ((a & 0xCCCC) >> 2) + (a & 0x3333);
a = ((a & 0xF0F0) >> 4) + (a & 0x0F0F);
a = ((a & 0xFF00) >> 8) + (a & 0x00FF);
printf("Have %i ones in binary", a);
return 0;
}
更多内容可以参考 Hacker’s Delight 一书。