Path: utzoo!attcan!uunet!husc6!rutgers!apple!desnoyer
From: desnoyer@Apple.COM (Peter Desnoyers)
Newsgroups: comp.lang.c
Subject: Re: assigning an integer to the negation of ...
Message-ID: <22651@apple.Apple.COM>
Date: 21 Dec 88 17:03:05 GMT
References: <1911@pembina.UUCP> <15090@mimsy.UUCP>
Organization: Apple Computer Inc, Cupertino, CA
Lines: 22

In article <15090@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes:
>In article <1911@pembina.UUCP> lake@alberta.UUCP (Robert Lake) writes:
>>		i = -(unsigned short)j;
>[where i is an int and j is 1---j's type is irrelevant]
>

It was pointed out that the context in which this problem arose was
TCP software - I would bet it was the window size calculations.
Quoting V. Jacobsen and R. Braden from RFC 1072 (TCP Extensions for
long-delay paths):

  The TCP header uses a 16 bit field to report the receive window size
  to the sender. Therefore, the largest window that can be used is 2**16
  = 65K bytes. (In practice, some TCP implementations will "break" for
  windows exceeding 2**15, because of their failure to do unsigned
  arithmetic.) 

I would also guess that the broken TCP implementations actually try to
do unsigned arithmetic, but don't get it right, as in the original,
subtly flawed example.

				Peter Desnoyers