decoder.py 文件源码

def _SignedVarintDecoder(bits, result_type):
  """Like _VarintDecoder() but decodes signed values."""

  signbit = 1 << (bits - 1)
  mask = (1 << bits) - 1

  def DecodeVarint(buffer, pos):
    result = 0
    shift = 0
    while 1:
      b = six.indexbytes(buffer, pos)
      result |= ((b & 0x7f) << shift)
      pos += 1
      if not (b & 0x80):
        result &= mask
        result = (result ^ signbit) - signbit
        result = result_type(result)
        return (result, pos)
      shift += 7
      if shift >= 64:
        raise _DecodeError('Too many bytes when decoding varint.')
  return DecodeVarint

# We force 32-bit values to int and 64-bit values to long to make
# alternate implementations where the distinction is more significant
# (e.g. the C++ implementation) simpler.