位运算

有符号右移（算数右移）保留符号位
int a = 16;
a:       00000000 00000000 00000000 00010000
a >> 2:  0000000000 00000000 00000000 000100

int b = -16;
b:       11111111 11111111 11111111 11110000
b >> 2:  1111111111 11111111 11111111 111100

无符号右移（逻辑右移）不保留符号位
unsigned int a = 16;
a:       00000000 00000000 00000000 00010000
a >> 2:  0000000000 00000000 00000000 000100

unsigned int a = -16;
a:       11111111 11111111 11111111 11110000
a >>2    0011111111 11111111 11111111 111100


int a = 100010101
int b = 011011011
int c = 001101011
int d = 101010101

异或为无进位二进制加法

a^b = c

x^x = 0
x = 100010101
x = 100010101

x^0 = x
x = 100010101
0 = 000000000

a^b = c
a^b^a = c^a
a^a^b = c^a
0^b = c^a
b = c^a