关于 0.1+0.2 == 0.30000000000000004 //true
0.1+0.2 == 0.3 //false
19.9*100 == 1989.9999999999998 //true
19.9*100 == 1990 //false
解决 (0.1*10+0.2*10)/10 == 0.3 //true
(19.9*10) * 100/10 == 1990 //true
