Is there a way to detect NaN and -NaN?

user_5697743 0
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I want to save lua number to string and handle NaN case correctly.

Detecting any NaN is easy, x ~= x.

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?

numbers nan lua
2 Answers

Instead of tostring(x) == 'nan', which is not portable, you can do the comparison with the actual tostring call: tostring(x) == tostring(0/0) or tostring(x) == tostring(-(0/0)) depending on what you need. If you need to do multiple comparisons, you can save the result of tostring and reuse it.

user_14429170

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

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

user_68346800
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