其他NaN值是什么？ [英] What are the other NaN values?

问题描述

文件c> java.lang.Double.NaN 表示它是

类型为 double 的非数字（NaN）值。它等于由 Double.longBitsToDouble（0x7ff8000000000000L）返回的值。

这似乎意味着还有其他的。如果是的话，我怎样才能得到他们，这可以做到portably？

要清楚，我想找到双 values x 这样



  Double。 doubleToRawLongBits（x）！= Double.doubleToRawLongBits（Double.NaN）
  

和

  Double.isNaN（x）
  





解决方案

您需要 doubleToRawLongBits 而不是 doubleToLongBits 。

$ b doubleToRawLongBits 提取实际的二进制表示。 doubleToLongBits 不会将所有的 NaN s转换为默认的 NaN

  double n = Double.longBitsToDouble（0x7ff8000000000000L）; //默认NaN 
 double n2 = Double.longBitsToDouble（0x7ff8000000000100L）; //也是NaN，但是M！= 0 
 
 System.out.printf（％X \ n，Double.doubleToLongBits（n））; 
 System.out.printf（％X \ n，Double.doubleToRawLongBits（n））; 
 System.out.printf（％X \ n，Double.doubleToLongBits（n2））; 
 System.out.printf（％X \ n，Double.doubleToRawLongBits（n2））; 
  

输出：

  7FF8000000000000 
 7FF8000000000000 
 7FF8000000000000 
 7FF8000000000100 
  

The documentation for java.lang.Double.NaN says that it is

A constant holding a Not-a-Number (NaN) value of type double. It is equivalent to the value returned by Double.longBitsToDouble(0x7ff8000000000000L).

This seems to imply there are others. If so, how do I get hold of them, and can this be done portably?

To be clear, I would like to find the double values x such that

Double.doubleToRawLongBits(x) != Double.doubleToRawLongBits(Double.NaN)

and

Double.isNaN(x)

are both true.

解决方案

You need doubleToRawLongBits rather than doubleToLongBits.

doubleToRawLongBits extracts the actual binary representation. doubleToLongBits doesn't, it converts all NaNs to the default NaN first.

double n = Double.longBitsToDouble(0x7ff8000000000000L); // default NaN
double n2 = Double.longBitsToDouble(0x7ff8000000000100L); // also a NaN, but M != 0

System.out.printf("%X\n", Double.doubleToLongBits(n));
System.out.printf("%X\n", Double.doubleToRawLongBits(n));
System.out.printf("%X\n", Double.doubleToLongBits(n2));
System.out.printf("%X\n", Double.doubleToRawLongBits(n2));

output:

7FF8000000000000
7FF8000000000000
7FF8000000000000
7FF8000000000100

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