In Lua, what is #INF and #IND?

Question

I\'m fairly new to Lua. While testing I discovered #INF/#IND. However, I can\'t find a good reference that explains it.

What are #INF

Answer 1

@YuHao has already pointed out what means +/-1.#INF (+-inf) and -1.#IND (nan), so I will just add how to deal with it (which I just needed to) in Lua:

• "inf" (+/- 1.#INF) are the higher number values that (Lua/C) can represent and the language provides that constant for you: "math.huge". So you can test a number inside Lua for +-INF; the function "isINF()" below shows how to use it.
• "nan" (- 1.#IND) is something that can not be handled numerically: it should be a number, its not, and anything you do with it is anything but a number also. with that in mind remember that no NaN is equal to other NaN; check for NaN like the function "isNAN()" below.

---

local function isINF(value)
  return value == math.huge or value == -math.huge
end

local function isNAN(value)
  return value ~= value
end

---

Answer 2

Expanding @YuHao already good answer.

Lua does little when converting a number to a string, since it heavily relies on the underlying C library implementation. In fact Lua print implementation calls Lua tostring which in turn (after a series of other calls) uses the lua_number2str macro, which is defined in terms of C sprintf. Thus in the end you see whatever representation for infinities and NaNs the C implementation uses (this may vary according to which compiler was used to compile Lua and which C runtime your application is linked to).

Answer 3

#INF is infinite, #IND is NaN. Give it a test:

print(1/0)
print(0/0)

Output on my Windows machine:

1.#INF
-1.#IND

As there's no standard representation for these in ANSI C, you may get different result. For instance:

inf
-nan