1、加減法block
a = a+b; b = a-b; a = a-b;
a = a+b;
b = a-b;
a = a-b;
2、乘除法
a = a*b; b = a/b; a = a/b;
a = a*b;
b = a/b;
a = a/b;
3、異或法
a = a^b; b = a^b; a = a^b;
a = a^b;
b = a^b;