TIS-100: Luhn Summation

function get_name()
  return "Luhn Summation"
end

function get_description()
  return { "ADD EVEN DIGITS.",
  "DOUBLE ODD DIGITS, IF DOUBLED IS GREATER THAN 9, SUBTRACT 9",
  "IF SUM MULTIPLE OF 10, WRITE 0, ELSE WRITE (10-UNIT DIGIT) TO CHK",
  "SEQUENCES ARE -1 TERMINATED"}
end

-- Luhn summation
function luhn( input, output, check, count)
  -- The first element in this sequence
  local head = #input + 1
  -- The last element in this sequence
  local tail = head + count - 1
  -- Sum of the number
  local sum = 0
  -- If true the number doubled
  local doDouble = true

  -- Generate the sequence
  for i = head,tail do
    -- Generate a number
    local inp = math.random( 0, 9 )
    -- Insert into the input
    table.insert( input, inp )
    -- Doubling?
    if( doDouble ) then
      inp = inp * 2
      -- Bigger than 9?
      if( inp > 9 ) then
        inp = inp - 9
      end
    end
    -- Add to sum
    sum = sum + inp
    -- Flip doubling flag
    doDouble = not doDouble
  end
  -- Append the sequence terminator
  table.insert( input, -1 )

  -- Add the sum, and terminator, to the output
  table.insert( output, sum )
  table.insert( output, -1 )

  -- Add check digit
  table.insert( check, ( sum * 9 % 10 ) )
  table.insert( check, -1 )
end

function get_streams()
  -- Maximum number of items to place into the input
  local MAX_COUNT = 38

  -- Numbers sent to the TIS-100
  input = {}

  -- Summations expected to get back from the TIS-100
  output = {}

  -- Check digits expected to get back from the TIS-100
  check = {}

  -- How many items are in the input
  local count = 0

  while( count < MAX_COUNT ) do
    -- Random sequence length
    local nextLen = math.random( 1, 8 )

    -- Update count
    count = count + nextLen + 1
    -- Bounds check
    if( count > MAX_COUNT ) then
      -- Too big, reduce sequence length
      nextLen = MAX_COUNT - ( count - nextLen - 1 )

      -- Set count to max
      count = MAX_COUNT
    end

    -- Add sequences to the input, and luhn sum to output
    luhn( input, output, check, nextLen )
  end

  return {
    { STREAM_INPUT, "IN.D", 1, input },
    { STREAM_OUTPUT, "OUT.CHK", 0, check },
    { STREAM_OUTPUT, "OUT.SUM", 2, output },
  }
end

function get_layout()
  return {
    TILE_COMPUTE,   TILE_COMPUTE, TILE_COMPUTE, TILE_COMPUTE,
    TILE_COMPUTE,   TILE_DAMAGED, TILE_COMPUTE, TILE_COMPUTE,
    TILE_COMPUTE,   TILE_COMPUTE, TILE_COMPUTE, TILE_COMPUTE,
  }
end