asda.nim

template unpackInt*(s: Stream, format: string): int =
  ## Unpack one or more bytes into an ``int``.
  ## The format can be "b", "B" or endiannes
  ## followed by input type: "<I", ">h", "!H"
  ##
  ## .. code-block:: nim
  ##    unpackInt("\x7f\xff", ">h") == 32767
  ##
  ## ====== ====================== ====
  ## symbol endianness             size
  ## ====== ====================== ====
  ## =      native
  ## <      little-endian
  ## >      big-endian
  ## !      network (big-endian)
  ## ====== ====================== ====
  ##
  ## ====== ====================== ====
  ## symbol input type             size
  ## ====== ====================== ====
  ## b      char                      1
  ## B      unsigned char             1
  ## h      short                     2
  ## H      unsigned short            2
  ## i      int                       4
  ## I      unsigned int              4
  ## l      long                      4
  ## L      unsigned long             4
  ## ==== ==== ====
  ##
  var result = 0
  case format[0]
  of 'b':
    result = s.readInt8.int

  of 'B':
    result = s.readUInt8.int

  of '=':
    case format[1]
    of 'h':
      result = s.readInt16.int
    of 'H':
      result = s.readUInt16.int
    else:
      discard

  of '<':
    var result: int
    case format[1]
    of 'h':
      var x = s.readInt16
      littleEndian16(addr x, addr x)
      result = x.int
    of 'H':
      var x = s.readUInt16
      littleEndian16(addr x, addr x)
      result = x.int
    of 'i', 'l':
      var x = s.readInt32
      littleEndian32(addr x, addr x)
      result = x.int
    of 'I', 'L':
      var x = s.readUInt32
      littleEndian32(addr x, addr x)
      result = x.int
    else:
      raise newException(Exception, "")

  of '>', '!':
    case format[1]
    of 'h':
      var x = s.readInt16
      bigEndian16(addr x, addr x)
      result = x.int
    of 'H':
      var x = s.readUInt16
      bigEndian16(addr x, addr x)
      result = x.int
    of 'i', 'l':
      var x = s.readInt32
      bigEndian32(addr x, addr x)
      result = x.int
    of 'I', 'L':
      var x = s.readUInt32
      bigEndian32(addr x, addr x)
      result = x.int
    else:
      raise newException(Exception, "")

  else:
    discard
  result