lua - How to get decimals to round down on the half

Question

I'm using this function to round currently:

function round(val, decimal)
  if (decimal) then
    return math.floor( (val * 10^decimal) + 0.5) / (10^decimal)
  else
    return math.floor(val+0.5)
  end
end

That function works perfectly except that when a number lands on .5 like 5.5 or 1000.5 or 7.5 I need it to round down instead of up. What changes would I have to make to the function to make that happen?

Answer 1

function round(val, decimal)
  local exp = decimal and 10^decimal or 1
  return math.ceil(val * exp - 0.5) / exp
end