What I'm curious about is: _what does XLC do?_
-- R; <><
On 04/28/16 19:15, Charles Mills wrote:
As a C/C++ convert, I like 0_0 (NULL in C lingo) better than FFFFFFFF_FFFFFFFF
(only because it is a widely-used convention in C). (OTOH FFF... is widely-used
in CMS.)
Agree with Gil's "collateral boon."
IBM should definitely standardize *something*, before we have 27 competing
"standards" out there.
Charles
-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf
Of Paul Gilmartin
Sent: Thursday, April 28, 2016 3:41 PM
To: [email protected]
Subject: Re: 64-bit caller and VL-bit
On Thu, 28 Apr 2016 14:23:14 -0700, Ed Jaffe wrote:
On 4/27/2016 8:25 PM, Phil Smith III wrote:
How does a 64-bit caller indicate the end of a variable parameter list?
We tend to use FFFFFFFF_FFFFFFFF as the end of list indicator. Yes, I
realize it's _technically_ a valid 64-bit address, but it's extremely
unlikely -- nee impossible -- that we would ever want to place a valid
parameter at that particular byte location in virtual storage. And, who
knows, maybe one day the z/OS guys will decide to make that last (1M or
2G) page guaranteed invalid like they do with the 4K page at 7FFFF000...
This has the collateral boon that you can code an empty 64-bit parameter list,
something not possible with a 24-bit or 31-bit parameter list.
But IBM should formalize the convention.
I believe it's part of the "C" standard that it should always be possible to
terminate a loop by testing for an address greater than that of any possible physical
object in storage.
And the UNIX argv[] vector is terminated by a NULL (0) pointer, not -1.
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