Lua math question: how to get rid of tiny reminder

Other
#1

The task is to check if the sum of angles of the triangle equals 180. After trigonometric calculations and summing the final result most likely there will be a result something like 180.0000000000000000001. Such a tiny bit is enough for the app to say that the triangle is not valid.
What is interesting:
print(summ_int) will give “180” in the console,
but
print(summ_int-180) will reveal this tiny thing as -2.8421709430404e-14 or any other…

At the moment I am using a work-around to get rid of this bit with the following two lines:

summ_int = tostring(summ_int)
summ_int = tonumber(summ_int)

I wonder is there a proper way of doing so?

#2

Would summ_int = math.round(summ_int) work? I’m not sure if that would remove the additional digits, or if you’d still have the same representation of the integer under the hood, meaning the .0000000000000000001 remains.

This is a general issue with floats, where you can end up with if (0.1+0.2 == 0.3) then returning false due to those “hidden” decimal places.

#3

Another approach is to measure the difference, for instance:

-- Used to prevent double float precision errors when comparing values to zero (0).
local zero = 1e-9

if math.abs(number1 - number2) < zero then
    ....
end

You can determine how precise you want the comparison to be.