Table of contents
The concept of bitwise operators:
Application of bitwise operators:
1. Application of & (bitwise AND):
2. Application of ^ (bitwise XOR):
The concept of bitwise operators:
There are three bitwise operators: & (bitwise and), | (bitwise or), ^ (bitwise exclusive or).
It should be noted that: the operand of the bit operator is an integer, and the specific implementation of the operation is the complement of two integers .
The concept of original code, complement code and inverse code:
(1) The original code, complement code, and inverse code of signed numbers are divided into two parts: the sign bit and the value bit. The sign bit is the first binary number, 0 means a positive number, and 1 means a negative number.
(2) The original code, complement code and inverse code of positive integers are the same .
(3) The original code of a negative integer is composed of the sign bit 1 and the corresponding value bit; the inverse code is that the sign bit of the original code remains unchanged, and the other bits are reversed bit by bit (0 becomes 1, 1 becomes 0); complement The code is inverse code +1.
1. & (Bitwise AND): If the binary bit corresponding to the complement of two integers is 0, it is 0, and if both are 1 at the same time, it is 1, and the obtained number is still the complement.
Take a chestnut:
//&（按位与）有0为0，同为1为1
int a = 1;// 补码为：00000000000000000000000000000001
int b = 2;// 补码为：00000000000000000000000000000010
int c = a & b;//补码为：00000000000000000000000000000000
//所以c的值为02. | (Bitwise OR): If the binary bit corresponding to the two's complement of two integers is 1, it is 1, and if both are 0 at the same time, it is 0, and the obtained number is still the complement.
Take a chestnut:
//|（按位或）有1为1，同为0为0
int a = 1;// 补码为：00000000000000000000000000000001
int b = 2;// 补码为：00000000000000000000000000000010
int c = a | b;//补码为：00000000000000000000000000000011
//所以c的值为33. ^ (bitwise XOR): The binary bits corresponding to the two’s complements of two integers are the same as 0, and the difference is 1, and the obtained number is still the complement.
Take a chestnut:
//^（按位异或）相同为0，相异为1
int a = 1;// 补码为：00000000000000000000000000000001
int b = 2;// 补码为：00000000000000000000000000000010
int c = a ^ b;//补码为：00000000000000000000000000000011
//所以c的值为3Application of bitwise operators:
1. Application of & (bitwise AND):
(1) Take the end of a certain binary number:
int a = 1;//补码：00000000000000000000000000000001
int tmp1 = a & 1;//此时tmp1的值为1
int b = 2;//补码：00000000000000000000000000000010
int tmp2 = a & 1;//此时tmp2的值为0For example, some topics require you to output the binary digits of a certain number bit by bit, then you can use the shift operator to achieve:
int main()
{
int a = 1;
int i = 0;
for (i = 0; i < 32; i++)
{
printf("%d", a & 1);
a >>= 1;
}
return 0;
}
(2) Make the rightmost 1 of a certain binary number disappear:
int n = 1;//n的补码：00000000000000000000000000000001
n = n & (n - 1);（n-1）的补码：00000000000000000000000000000000
//结果n的补码：000000000000000000000000000000002. Application of ^ (bitwise XOR):
An interview question: Swap two numbers without creating a temporary variable.
Generally, if you want to exchange two numbers, you can do this:
tmp = num2;
num2 = num1;
num1 = tmp;If you create a temporary variable, there is actually another way:
num1 = num1 + num2;
num2 = num1 - num2;
num1 = num1 - num2;So how to use ^ (bitwise XOR) to realize variable exchange, in fact, the operation rule of ^ (bitwise XOR) satisfies the exchange law, for example:
a ^ a = 0;
a ^ 0 = a;
a ^ b ^ a = b;//先运算a ^ a = 0;在运算0 ^ b = b;
//可以理解为(a ^ a) ^ b = b;From this we can know:
a = a ^ b;
b = a ^ b;
a = a ^ b;Draw a picture:
This method is very clever, but it is not very practical, and its efficiency is not even as high as creating temporary variables, but it can give you a better understanding of bit operators that may achieve some zero operations that you did not expect.