On Mon, 29 Jan 2007 21:31:36 +0000
David Laight <david@l8s.co.uk> wrote:


> 
> Historically a byte read from address 0 returned the value 0, so that
> code could do 'if (*ptr)' instead of 'if (ptr && *ptr)' in order to
> save code bytes.
> 
That depends on how historical you want to get.  On PDP-11s, 0 was the
start of the text segment, and was where the kernel branched after an
exec.  From a.out(5) from 7th Edition Unix:

	The text segment begins at 0 in the core image; the  header
	is not loaded.

I confess I do not remember the optimization you refer to.


		--Steve Bellovin, http://www.cs.columbia.edu/~smb