Runtime Fast Bitbuffer

Reader.lua

local Reader = {}
Reader.__index = Reader

local function nextChunk(reader, width)
	local value
	if width > 24 then
		reader._chunk += buffer.readu32(reader._buffer, reader._byte) * 2^reader._bit

		reader._byte += 4
		reader._bit += 32
	elseif width > 16 then
		reader._chunk += ( buffer.readu8(reader._buffer, reader._byte)
			+ buffer.readu16(reader._buffer, reader._byte + 1) * 2^8 ) * 2^reader._bit

		reader._byte += 3
		reader._bit += 24
	elseif width > 8 then
		reader._chunk += buffer.readu16(reader._buffer, reader._byte) * 2^reader._bit

		reader._byte += 2
		reader._bit += 16
	else
		reader._chunk += buffer.readu8(reader._buffer, reader._byte) * 2^reader._bit

		reader._byte += 1
		reader._bit += 8
	end
end

function Reader.new(b: buffer)
	return setmetatable({
		_buffer = b,
		_byte = 0,
		_bit = 0,
		_chunk = 0
	}, Reader)
end

function Reader:UInt(width: number): number
	if self._bit < width then
		nextChunk(self, width - self._bit)
	end

	local value = self._chunk % 2^width

	self._chunk //= 2^width
	self._bit -= width

	return value
end

return Reader

Writer.lua

local Writer = {}
Writer.__index = Writer

local function depositChunk32(writer)
	buffer.writeu32(writer._buffer, writer._byte, writer._chunk)
	writer._chunk //= 2^32

	writer._byte += 4
	writer._bit -= 32
end

local function depositChunk(writer)
	if writer._bit > 32 then
		depositChunk32(writer)
	elseif writer._bit > 24 then
		buffer.writeu8(writer._buffer, writer._byte, writer._chunk)
		buffer.writeu16(writer._buffer, writer._byte + 1, writer._chunk // 2^8)
		writer._chunk //= 2^24

		writer._byte += 3
		writer._bit -= 24
	elseif writer._bit > 16 then
		buffer.writeu16(writer._buffer, writer._byte, writer._chunk)
		writer._chunk //= 2^16

		writer._byte += 2
		writer._bit -= 16
	else
		buffer.writeu8(writer._buffer, writer._byte, writer._chunk)
		writer._chunk //= 2^8

		writer._byte += 1
		writer._bit -= 8
	end
end

function Writer.new(b: buffer)
	return setmetatable({
		_buffer = b,
		_byte = 0,
		_bit = 0,
		_chunk = 0
	}, Writer)
end

function Writer:UInt(value: number, width: number)
	local nextBit = self._bit + width

	if nextBit > 53 then
		depositChunk(self)
		nextBit = self._bit + width
	end

	self._chunk += value * 2^self._bit
	self._bit = nextBit
end

function Writer:Close()
	while self._bit > 0 do
		depositChunk(self)
	end
end

return Writer