round.lua

local uptime = os.clock
local n = 1000000

--------------

local function round1(num)
    return num + (2 ^ 52 + 2 ^ 51) - (2 ^ 52 + 2 ^ 51)
end

start = uptime()

for i = 1, n do
  round1(1.234)
end

print("Constant ", uptime() - start)

--------------

local huge = 2 ^ 52 + 2 ^ 51

local function round2(num)
    return num + huge - huge
end

start = uptime()

for i = 1, n do
  round2(1.234)
end

print("Upvalue ", uptime() - start)

--------------

start = uptime()

for i = 1, n do
  math.floor(1.234 + 0.5)
end

print("math.floor", uptime() - start)

--------------

local floor = math.floor

start = uptime()

for i = 1, n do
  floor(1.234 + 0.5)
end

print("floor (no indexing)", uptime() - start)

--------------

local function round3(num)
	return (num + 0.5) // 1
end

start = uptime()

for i = 1, n do
  round3(1.234)
end

print("Lua 5.3+: (num + 0.5) // 1 ", uptime() - start)

--------------

local function round4(num)
	num = num + 0.5
	return num - num % 1
end

start = uptime()

for i = 1, n do
  round4(1.234)
end

print("Lua 5.2+: num - num % 1 ", uptime() - start)