function struct.unpack()

in lib/shenyu/register/core/struct.lua [115:202]

• 75 lines of code
• 18 McCabe index (conditional complexity)

function struct.unpack(format, stream, pos)
  local vars = {}
  local iterator = pos or 1
  local endianness = true

  for i = 1, format:len() do
    local opt = format:sub(i, i)

    if opt == "<" then
      endianness = true
    elseif opt == ">" then
      endianness = false
    elseif opt:find("[bBhHiIlL]") then
      local n = opt:find("[hH]") and 2 or opt:find("[iI]") and 4 or opt:find("[lL]") and 8 or 1
      local signed = opt:lower() == opt

      local val = 0
      for j = 1, n do
        local byte = string.byte(stream:sub(iterator, iterator))
        if endianness then
          val = val + byte * (2 ^ ((j - 1) * 8))
        else
          val = val + byte * (2 ^ ((n - j) * 8))
        end
        iterator = iterator + 1
      end

      if signed and val >= 2 ^ (n * 8 - 1) then
        val = val - 2 ^ (n * 8)
      end

      table.insert(vars, math.floor(val))
    elseif opt:find("[fd]") then
      local n = (opt == "d") and 8 or 4
      local x = stream:sub(iterator, iterator + n - 1)
      iterator = iterator + n

      if not endianness then
        x = string.reverse(x)
      end

      local sign = 1
      local mantissa = string.byte(x, (opt == "d") and 7 or 3) % ((opt == "d") and 16 or 128)
      for i = n - 2, 1, -1 do
        mantissa = mantissa * (2 ^ 8) + string.byte(x, i)
      end

      if string.byte(x, n) > 127 then
        sign = -1
      end

      local exponent =
        (string.byte(x, n) % 128) * ((opt == "d") and 16 or 2) +
        math.floor(string.byte(x, n - 1) / ((opt == "d") and 16 or 128))
      if exponent == 0 then
        table.insert(vars, 0.0)
      else
        mantissa = (math.ldexp(mantissa, (opt == "d") and -52 or -23) + 1) * sign
        table.insert(vars, math.ldexp(mantissa, exponent - ((opt == "d") and 1023 or 127)))
      end
    elseif opt == "s" then
      local bytes = {}
      for j = iterator, stream:len() do
        if stream:sub(j, j) == string.char(0) or stream:sub(j) == "" then
          break
        end

        table.insert(bytes, stream:sub(j, j))
      end

      local str = table.concat(bytes)
      iterator = iterator + str:len() + 1
      table.insert(vars, str)
    elseif opt == "c" then
      local n = format:sub(i + 1):match("%d+")
      local len = tonumber(n)
      if len <= 0 then
        len = table.remove(vars)
      end

      table.insert(vars, stream:sub(iterator, iterator + len - 1))
      iterator = iterator + len
      i = i + n:len()
    end
  end

  return vars, iterator
end