Integer division using "bitwise ops", long division approach instead of iterated subtraction

main.lua

-- Tested on repl.it

local N = 8 -- or 16, etc. Could also adapt for fixed point

local lshift = math.ldexp
local HighBitMask = lshift(1, N - 1)

local function Div (a, b)
  local acc, result = 0, 0
  local mask = HighBitMask -- one-hot mask

  for _ = 1, N do
    result = 2 * result -- left shift
                        -- will be 0 on first pass
                        -- avoids over-shift at end

    if a >= mask then -- bit set?
      a = a - mask -- clear bit (since using >= operator)
      acc = acc + 1 -- or in 1 bit
    end

    if acc >= b then
      acc = acc - b
      result = result + 1 -- or in 1 bit
    end

    acc = 2 * acc -- left shift
    mask = .5 * mask -- right shift
  end

  return result
end

local NN = 0

local function Print (a, b)
  if NN < 100 then
    print("Discrepancy at", a, ", ", b)

    NN = NN + 1
  end
end

local floor = math.floor

for a = 0, 255 do
  for b = 1, 255 do
    if Div(a, b) ~= floor(a / b) then
      Print(a, b)
    end
  end
end

print(NN > 0 and "Finished with problems" or "OK!")