Lua:
Rounding numbers
How to:
-- Basic rounding in Lua doesn't come built-in, but you can define a function:
function round(num)
return num >= 0 and math.floor(num + 0.5) or math.ceil(num - 0.5)
end
print(round(3.5)) -- 4
print(round(2.3)) -- 2
print(round(-1.6)) -- -2
-- To round to a specific decimal place:
function round(num, decimalPlaces)
local mult = 10^(decimalPlaces or 0)
return math.floor(num * mult + 0.5) / mult
end
print(round(3.14159, 2)) -- 3.14
print(round(1.98765, 3)) -- 1.988Deep Dive
Lua doesn’t include a round function out of the box unlike some other languages. Historically, you need to write your own or use a third-party library. Common workarounds rely on math.floor() for rounding down and math.ceil() for rounding up, coupled with adding or subtracting 0.5 before doing so, depending on the number’s sign.
Alternatives to rolling your own function include libraries such as “lua-users wiki” or “Penlight”. Each has its benefits and trade-offs, like additional features or more overhead.
Internally, these functions normally work by exploiting the way computers store floating-point numbers. Adding 0.5 to a positive float that you want to round will push it over the threshold of the next integer value, so when you apply math.floor() it rounds down to that nearest integer.