Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!pilchuck!dataio!fnx!nazgul!bright
From: bright@nazgul.UUCP (Walter Bright)
Newsgroups: comp.lang.c
Subject: Re: What breaks? (was Re: 64 bit longs?)
Message-ID: <230@nazgul.UUCP>
Date: 19 Jan 91 07:22:19 GMT
References: <2567@casbah.acns.nwu.edu> <1991Jan13.220958.16568@zoo.toronto.edu> <54379@eerie.acsu.Buffalo.EDU>
Reply-To: bright@nazgul.UUCP (Walter Bright)
Organization: Zortech, Seattle
Lines: 20

In article <54379@eerie.acsu.Buffalo.EDU> chu@acsu.buffalo.edu (john c chu) writes:
/In article <1991Jan13.220958.16568@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes:
/>It is intuitively appealing, but I would be surprised to see anyone
/>implementing it:  it would break far too much badly-written software.
/Can someone please tell me what would break under that model and why?
/It's not that I don't believe it, or that I want to write code that
/will break. It's that I want to avoid making the unwarranted
/assumptions that would lead to my code breaking.

Code that will break:
	char *p;
	unsigned long x;
	...
	/* Read 4 bytes out of buffer */
	x = *(unsigned long*)p;  /* assume bytes are in correct order */
Also:
	x >>= 24;
	/* Now assume that x < 256 */
Also:
	x &= 0xFFFFFFFE;	/* clear bit 0 */