File IO & Bits

The Renoise API uses Lua's standard io library to read or write external files.

To access the raw bits and bytes of some data, for example, to read or write binary file streams, you can use the bit library. It's built into the Renoise API, so there's no need to require it.

See the LuaJIT bit library documentation for more info and examples.

-- Reading integer numbers or raw bytes from a file

local function read_word(file)
  local bytes = file:read(2)
  if (not bytes or #bytes < 2) then 
    return nil 
  else
    -- little-endian
    return bit.bor(bytes:byte(1),
      bit.lshift(bytes:byte(2), 8))
  end
end

local function read_dword(file)
  local bytes = file:read(4)
  if (not bytes or #bytes < 4) then 
    return nil 
  else
    -- little-endian
    return bit.bor(bytes:byte(1),
      bit.lshift(bytes:byte(2), 8),
      bit.lshift(bytes:byte(3), 16),
      bit.lshift(bytes:byte(4), 24))  
  end   
end

-- and so on (adapt as needed to deal with endianness!) ...

local file, err = io.open("some_binary_file.bin", "rb")
if not file then
  print("Could not open file: " .. tostring(err))
  return
end

local bytes = file:read(512)

if (not bytes or #bytes < 512) then 
  print("unexpected end of file")
else
  for i = 1, #bytes do
    print(bytes:byte(i))
  end
end
    
print(read_word(file) or "unexpected end of file")
print(read_dword(file) or "unexpected end of file")

file:close()