浮點數的標準可以看百度百科:http://baike.baidu.com/view/1698149.htm
NaN :階碼的每個二進制位全爲1 並且 尾數不爲0;
無窮:階碼的每個二進制位全爲1 並且 尾數爲0;符號位爲0,是正無窮,符號位爲1是負無窮。
所以NaN、正無窮、負無窮可以如此定義,可以如此判斷是否NaN:
//float
int __NaN=0xFFC00000,__Infinity=0x7F800000,__Neg_Infinity=0xFF800000;
const float NaN=*((float *)&__NaN),Infinity=*((float *)&__Infinity),Neg_Infinity=*((float *)&__Neg_Infinity);
bool IsNaN(float dat)
{
int & ref=*(int *)&dat;
return (ref&0x7F800000) == 0x7F800000 && (ref&0x7FFFFF)!=0;
}
//double
__int64 __NaN=0xFFF8000000000000,__Infinity=0x7FF0000000000000,__Neg_Infinity=0xFFF0000000000000;
const double NaN=*((double *)&__NaN),Infinity=*((double *)&__Infinity),Neg_Infinity=*((double *)&__Neg_Infinity);
bool IsNaN(double dat)
{
__int64 & ref=*(__int64 *)&dat;
return (ref&0x7FF0000000000000) == 0x7FF0000000000000 && (ref&0xfffffffffffff)!=0;
}