其他 NaN 值是什么？

发布于 2024-08-19 10:52:58 字数 539 浏览 2 评论 0原文

保存双精度型非数字 (NaN) 值的常量。它相当于 Double.longBitsToDouble(0x7ff8000000000000L) 返回的值。

这似乎暗示还有其他人。如果是这样，我如何获得它们，这可以便携地完成吗？

需要明确的是，我想找到 double 值 x 使得

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

和

Double.isNaN(x)

都为真。

原文

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.

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千鲤 2024-08-26 10:52:58

您需要 doubleToRawLongBits 而不是 doubleToLongBits。

doubleToRawLongBits 提取实际的二进制表示形式。 doubleToLongBits 不会，它首先将所有 NaN 转换为默认的 NaN。

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));

输出：

7FF8000000000000
7FF8000000000000
7FF8000000000000
7FF8000000000100

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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放低过去 2024-08-26 10:52:58

Java 使用 IEEE 754 作为其浮点数，因此遵循其规则。

根据 NaN 的维基百科页面，它的定义如下：

IEEE 浮点标准单精度 NaN 的逐位示例：x111 1111 1axx xxxx xxxx xxxx xxxx xxxx 其中 x 表示 不照顾。

因此有相当多的位模式都是 NaN 值。

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假扮的天使 2024-08-26 10:52:58

IEEE 754 将 NaN 定义为所有指数位均为 1 且尾数为非零数的数字。

因此，对于您正在寻找的单精度数字：

S     E            M
x  11111111   xxxxxx....xxx (with M != 0)

Java 是这样处理的：

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

System.out.println(n.isNaN()); // true
System.out.println(n2.isNaN()); // true
System.out.println(n2 != Double.doubleToLongBits(Double.NaN)); // true

总而言之，您可以使用任何符合上述规则的 NaN（指数中的所有位都为 1，尾数！= 0）。

IEEE 754 defines a NaN as a number with all exponent bits which are 1 and a non zero number in the mantissa.

So for a single-precision number you are looking for:

S     E            M
x  11111111   xxxxxx....xxx (with M != 0)

Java handles this like so:

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

System.out.println(n.isNaN()); // true
System.out.println(n2.isNaN()); // true
System.out.println(n2 != Double.doubleToLongBits(Double.NaN)); // true

To sum, you can use any NaN you want which conforms to the rules aforementioned (all bits 1 in exponent and mantissa != 0).

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