def _FloatDecoder():
  """Returns a decoder for a float field.

  This code works around a bug in struct.unpack for non-finite 32-bit
  floating-point values.
  """

  local_unpack = struct.unpack

  def InnerDecode(buffer, pos):
    # We expect a 32-bit value in little-endian byte order.  Bit 1 is the sign
    # bit, bits 2-9 represent the exponent, and bits 10-32 are the significand.
    new_pos = pos + 4
    float_bytes = buffer[pos:new_pos]

    # If this value has all its exponent bits set, then it's non-finite.
    # In Python 2.4, struct.unpack will convert it to a finite 64-bit value.
    # To avoid that, we parse it specially.
    if (float_bytes[3:4] in b'\x7F\xFF' and float_bytes[2:3] >= b'\x80'):
      # If at least one significand bit is set...
      if float_bytes[0:3] != b'\x00\x00\x80':
        return (_NAN, new_pos)
      # If sign bit is set...
      if float_bytes[3:4] == b'\xFF':
        return (_NEG_INF, new_pos)
      return (_POS_INF, new_pos)

    # Note that we expect someone up-stack to catch struct.error and convert
    # it to _DecodeError -- this way we don't have to set up exception-
    # handling blocks every time we parse one value.
    result = local_unpack('<f', float_bytes)[0]
    return (result, new_pos)
  return _SimpleDecoder(wire_format.WIRETYPE_FIXED32, InnerDecode)
Returns a decoder for a float field.

  This code works around a bug in struct.unpack for non-finite 32-bit
  floating-point values.