gistfile1.lua

function _M.encode_binary_length(len)
	return (math.ceil(tonumber(len) / 7) * 8) + 1
end
local encode_masks = {
	{0x01, 0xfc},
	{0x03, 0xf8},
	{0x07, 0xf0},
	{0x0f, 0xe0},
	{0x1f, 0xc0},
	{0x3f, 0x80},
}
function _M.encode_binary(bin, len, out, olimit)
	-- encode with every 7 byte chunk
	local src = ffi.cast('const uint8_t *', bin)
	local ret = out
	local idx = 0
	local olen = 0
	if olimit < _M.encode_binary_length(len) then
		assert(false, "output buffer too short")
	end
	while idx < len do
		--[[
			0 :                      (curr & 0xfe) >> 1
			1 : (prev & 0x01) << 6 + (curr & 0xfc) >> 2
			2 : (prev & 0x03) << 5 + (curr & 0xf8) >> 3
			3 : (prev & 0x07) << 4 + (curr & 0xf0) >> 4
			4 : (prev & 0x0f) << 3 + (curr & 0xe0) >> 5
			5 : (prev & 0x1f) << 2 + (curr & 0xc0) >> 6
			6 : (prev & 0x3f) << 1 + (curr & 0x80) >> 7
			7 : (prev & 0x7f)
		]]
		ret[olen] = bit.rshift(bit.band(src[idx], 0xfe), 1) + 0x80; olen = olen + 1
		for i=1,6 do
			local prev = src[idx + i - 1]
			if (idx + i) >= len then
				ret[olen] = bit.lshift(bit.band(prev, encode_masks[i][1]), 7 - i) + 0x80; olen = olen + 1
				goto LAST
			end
			local curr = src[idx + i]
			local payload 
				= bit.lshift(bit.band(prev, encode_masks[i][1]), 7 - i)
				+ bit.rshift(bit.band(curr, encode_masks[i][2]), i + 1)
			ret[olen] = payload + 0x80; olen = olen + 1
		end
		ret[olen] = bit.band(src[idx + 6], 0x7f) + 0x80; olen = olen + 1
		idx = idx + 7
	end
::LAST::
	ret[olen] = 0x00; olen = olen + 1
	return ret, olen
end
local decode_masks = {
	{0x7f, 0x40},
	{0x3f, 0x60},
	{0x1f, 0x70},
	{0x0f, 0x78},
	{0x07, 0x7c},
	{0x03, 0x7e},
	{0x01, 0x7f},
}
function _M.decode_binary(bin, limit, out, olimit)
	-- encode with every 7 byte chunk
	local src = ffi.cast('const uint8_t *', bin)
	local limit = limit or (10 * 1000 * 1000 * 1000)
	local ret = out
	local idx = 0
	local olen = 0
	if src[idx] == 0x00 then
		return ret, 0, 1
	end
	while idx < limit do
		--[[
			0 : (curr & 0x7f) << 1 + (next & 0x40) >> 6
			1 : (curr & 0x3f) << 2 + (next & 0x60) >> 5
			2 : (curr & 0x1f) << 3 + (next & 0x70) >> 4 
			3 : (curr & 0x0f) << 4 + (next & 0x78) >> 3
			4 : (curr & 0x07) << 5 + (next & 0x7c) >> 2
			5 : (curr & 0x03) << 6 + (next & 0x7e) >> 1
			6 : (curr & 0x01) << 7 + (next & 0x7f) >> 0
		]]
		if src[idx] == 0x00 then
			return ret, olen, idx + 1
		end
		for i=0,6 do
			local curr, nxt = src[idx + i], src[idx + i + 1]
			if nxt == 0x00 then
				return ret, olen, idx + i + 2
			end
			-- print(i, src[idx + 1], header, bit.band(header, bit.lshift(1, 7 - i)) ~= 0, bit.band(src[idx + i], 0x7f))
			local payload 
				= bit.lshift(bit.band(curr, decode_masks[i + 1][1]), i + 1) 
				+ bit.rshift(bit.band(nxt, decode_masks[i + 1][2]), 6 - i)
			-- print('payload', i, ('%02x'):format(payload))
			ret[olen] = payload; olen = olen + 1
		end
		idx = idx + 8
	end
	print(idx, limit)
	assert(false, "should not reach here")
end