两个浮点数比较大小方法
a>b if( (a-b) > EPSINON)
a<b if( (a-b) <-EPSINON)
a>=b if( (a-b) >= -EPSINON)
a<=b if( (a-b) <= EPSINON)
a==b if ((a-b>=-EPSINON) && (a-b<=EPSINON))
a<b if( (a-b) <-EPSINON)
a>=b if( (a-b) >= -EPSINON)
a<=b if( (a-b) <= EPSINON)
a==b if ((a-b>=-EPSINON) && (a-b<=EPSINON))