有没有办法检测 NaN 和 -NaN? [英] Is there a way to detect NaN and -NaN?

问题描述

我想将 lua 数字保存为字符串并正确处理 NaN 大小写.

I want to save lua number to string and handle NaN case correctly.

检测任何 NaN 很容易，x ~= x.

Detecting any NaN is easy, x ~= x.

但是，我发现只有一种检测方法是 NaN 或 -NaN 是使用 tostring(x) == 'nan'.有没有更好的方法?

However, only one way which I've found to detect is it NaN or -NaN is to use tostring(x) == 'nan'. Is there a better way to do it?

推荐答案

存在两个以上的 NaN(实际上，根据 IEEE-754，有 2^52-1 个 NaN).
它们的 tostring 表示依赖于平台.
这是如何获得三个不同的 NaN 的示例(我使用的是用 Visual Studio 构建的 Lua 5.3):

There are more than two NaNs exist (actually, there are 2^52-1 NaNs according to IEEE-754).
Their tostring-ed representations are platform-dependent.
This is an example how to get three different NaNs (I'm using Lua 5.3 built with Visual Studio):

n = string.unpack(">d", string.pack(">d", 0/0):sub(1, -2).."@")
print(0/0, -(0/0), n) -->  -1.#IND   1.#QNAN   -1.#QNAN

因此，不区分 NaN 的不同变体会更正确.

So, it would be more correct to not distinguish between different variants of NaN.

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