Simple Round

wiki

function round(num, idp)
  local mult = 10^(idp or 0)
  return math.floor(num * mult + 0.5) / mult
end

Here is an alternative implementation:

function round2(num, idp)
  return tonumber(string.format("%." .. (idp or 0) .. "f", num))
end

Both are Lua 5.0 and 5.1 compatible.

Tests:

> function test(a, b) print(round(a,b), round2(a,b)) end
> test(43245325.9995, 3)
43245326        43245325.999
> test(43245325.9994, 3)
43245325.999    43245325.999
> test(43245325.5543654)
43245326        43245326
> test(43245325.5543654, 3)
43245325.554    43245325.554
> test(43245325.5543654, 4)
43245325.5544   43245325.5544