Biggest integer in Gideros 2015.12 Lua 5.1

totebo · February 2016

I am looking to use the largest number available in Lua. I assumed this number would be 2,147,483,647 (signed 32 bit Int) or 4,294,967,295 (unsigned 32 bit Int). After a little testing it appears to be 99,999,999,999,999. It's a lot better of course, but can someone explain why this is the biggest number?

This is how I tested:

print(99999999999999)   -- 99999999999999
print(99999999999999.1) -- 99999999999999
print(9999999999999.9)  -- 9999999999999.9
print(100000000000000)  -- 1e+14

antix · February 2016

I think LUA uses a 53 bit number, so 2^53 would be the biggest integer you could have.

I also discovered recently that sometimes when doing math you can get the result -0.0 which causes lots of bother. In that case you can check vs the following... 2^-53

tkhnoman · February 2016

It's actually not the biggest, 1e+14 is just because lua use rounding (it's not error, you can still process it)

You can always process the data like the old days, so if it exceed that 1e+14, simply put big numbers at another variable, and mod it.

hgy29 · February 2016

It is because Lua numbers are not ints, but double precision floats, with a 53 bits mantissa. https://en.m.wikipedia.org/wiki/Double-precision_floating-point_format

totebo · February 2016

That's great information guys, thanks! So, which IS the largest number you can perform operations on!?

SinisterSoft · February 2016

You mean the largest int ?

ar2rsawseen · February 2016

https://www.wolframalpha.com/input/?i=2^52

totebo · February 2016

Bingo! An answer veiled in mystery. Nice site @ar2.

Drumroll...

4,503,599,627,370,496

antix · February 2016

So that's how many sprites you think you are going to have onscreen at once?

totebo · February 2016

Yeah, should be cool, no?

hgy29 · February 2016

Actually the biggest integer you can store is 1.7976931348623157 × 10^308, since this was your original question, but the only operations you can do on it without losing information is dividing it by 2 or substracting another number with the same exponent...

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