From owner-sc22wg14+sc22wg14-domo2=www.open-std.org@open-std.org  Fri Oct 23 06:14:22 2015
Return-Path: <owner-sc22wg14+sc22wg14-domo2=www.open-std.org@open-std.org>
X-Original-To: sc22wg14-domo2
Delivered-To: sc22wg14-domo2@www.open-std.org
Received: by www.open-std.org (Postfix, from userid 521)
	id AEF1B357126; Fri, 23 Oct 2015 06:14:22 +0200 (CEST)
Delivered-To: sc22wg14@open-std.org
Received: from mail-qk0-f172.google.com (mail-qk0-f172.google.com [209.85.220.172])
	(using TLSv1 with cipher RC4-SHA (128/128 bits))
	(No client certificate requested)
	by www.open-std.org (Postfix) with ESMTP id 43603356DEA
	for <sc22wg14@open-std.org>; Fri, 23 Oct 2015 06:14:22 +0200 (CEST)
Received: by qkca6 with SMTP id a6so66162206qkc.3
        for <sc22wg14@open-std.org>; Thu, 22 Oct 2015 21:14:21 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=gmail.com; s=20120113;
        h=message-id:date:from:user-agent:mime-version:to:subject
         :content-type:content-transfer-encoding;
        bh=Zm5Dz9R0aNXyXwE7htWorpPun1nJWJC6uFVg5ttKeaw=;
        b=rKKphcE40dNephX5xtROGm2Oo6+Op/pClm1DJXG9+J+9qAtWvUszXiHkclkKdZs6ft
         JwI8hVeXM+4nDGJ0eddC2kGUFaWwFB5f80tXZNYKxUR6/RcuFG3CA0q/NNjln98/zXSk
         0QNNsC7QetOB6yrX8Rb5uuG1weLHqhyqzbjsKIy1zY0UPymImpTXO+Xd7s05OVIRTNaY
         koZg5PXpfj/VndWyLc3Fk4GXE23qjVSJSdwgICYZktnTjS4CXrzkedoGnzcriBpyKBJw
         VHBcN/ReoL2qYuhXvXKWAMhh/tIWqZzlWBfhMcnWaSb0Tt2eERPSENPt0qCMUGwMnDun
         M1Sw==
X-Received: by 10.140.19.13 with SMTP id 13mr22860859qgg.97.1445573660874;
        Thu, 22 Oct 2015 21:14:20 -0700 (PDT)
Received: from [192.168.0.26] (70-59-0-242.hlrn.qwest.net. [70.59.0.242])
        by smtp.gmail.com with ESMTPSA id n48sm6727850qgd.35.2015.10.22.21.14.19
        for <sc22wg14@open-std.org>
        (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
        Thu, 22 Oct 2015 21:14:20 -0700 (PDT)
Message-ID: <5629B41A.3000601@gmail.com>
Date: Thu, 22 Oct 2015 22:14:18 -0600
From: Martin Sebor <msebor@gmail.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0
MIME-Version: 1.0
To: "sc22wg14@open-std.org" <sc22wg14@open-std.org>
Subject: atomic_fetch and modify generic functions
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Sender: owner-sc22wg14@open-std.org
Precedence: bulk

Back in 7.17.1, in paragraph 5, there is the text parts of which
I quoted in my previous post:

   In the following synopses:
   -- An A refers to one of the atomic types.
   -- A C refers to its corresponding non-atomic type.
   -- An M refers to the type of the other argument for arithmetic
      operations. For atomic integer types, M is C.
      For *atomic pointer types*, M is ptrdiff_t.

Looking through section 7.17 to see where M is used, I find only
one.  It says this:

   7.17.7.5 The atomic_fetch and modify generic functions

   The following operations perform arithmetic and bitwise
   computations. All of these operations are applicable
   to an object of any *atomic integer type*. None of these
   operations is applicable to atomic_bool.

but then in the Description section of atomic_fetch:

     For signed integer types... For address types, the result
     may be an undefined address, but the operations otherwise
     have no undefined behavior

It looks like the middle paragraph is incorrect or incomplete
and the functions are applicable objects of atomic integer
types and atomic pointer types.

In addition, what exactly does it mean for an operation to be
applicable to a type? Is it ill-formed to use it with a different
type (i.e., is a diagnostic required). Or is it undefined?

FWIW, the implementations I have tested accept atomic _Bool
and atomic pointer types in addition to atomic integers. One
also accepts non-atomic integers.

Martin