[Cfp-interest 2357] Re: Updated (V7) N2823
Rajan Bhakta
rbhakta at us.ibm.com
Thu Jan 20 08:02:31 PST 2022
Addressing all of Jim's and Fred's comments. Note that I do intend to
update this one time at the end to add in better structure (title, author,
revision number, etc. as the heading) and summarizing the reflector
messages as Jens asked in the motivation section.
(See attached file: N2823UpdateV7.html)
Regards,
Rajan Bhakta
z/OS XL C/C++ Compiler Technical Architect
ISO C Standards Representative (Canada, USA), PL22.11 Chair
C/C++ Compiler Development
rbhakta at us.ibm.com
IBM
From: "Jim Thomas" <jaswthomas at sbcglobal.net>
To: "Rajan Bhakta" <rbhakta at us.ibm.com>
Cc: "CFP" <cfp-interest at ucbtest.org>
Date: 01/20/2022 12:24 AM
Subject: [EXTERNAL] Re: [Cfp-interest 2346] Updated (V4) N2823
Rajan, the comments below are for V4. I believe most of them still apply to
V6, but they are incomplete. It will probably be Friday before I can
respond to V6 properly. How tight is your schedule on this? On Jan 19,
2022, at 3:25 PM, Rajan Bhakta ZjQcmQRYFpfptBannerStart
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Rajan, the comments below are for V4. I believe most of them still apply to
V6, but they are incomplete. It will probably be Friday before I can
respond to V6 properly. How tight is your schedule on this?
On Jan 19, 2022, at 3:25 PM, Rajan Bhakta <rbhakta at us.ibm.com> wrote:
Once more into the breech! Responses inline in blue below.
(See attached file: N2823UpdateV6.html)
Regards,
Rajan Bhakta
z/OS XL C/C++ Compiler Technical Architect
ISO C Standards Representative (Canada, USA), PL22.11 Chair
C/C++ Compiler Development
rbhakta at us.ibm.com
IBM
<graycol.gif>"Jim Thomas" ---01/19/2022 04:26:12 PM---There’s no need
to mention <math.h> in “… when <stdlib.h>, <fenv.h> and <math.h> are
included …”. Th
From: "Jim Thomas" <jaswthomas at sbcglobal.net>
To: "Rajan Bhakta" <rbhakta at us.ibm.com>
Cc: "CFP" <cfp-interest at ucbtest.org>
Date: 01/19/2022 04:26 PM
Subject: [EXTERNAL] Re: [Cfp-interest 2346] Updated (V4) N2823
There’s no need to mention <math.h> in “… when <stdlib.h>, <fenv.h>
and <math.h> are included …”. The “inclusive version” of Alternative
1 is missing ", without the requirements to set errno (see 7.5) or
modify the floating-point ZjQcmQRYFpfptBannerStart
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There’s no need to mention <math.h> in “… when <stdlib.h>, <fenv.h>
and <math.h> are included …”.
Agreed.
The “inclusive version” of Alternative 1 is missing ", without the
requirements to set errno (see 7.5) or modify the floating-point
environment (see 7.6),”.
I thought that was the discussion we had today. Without requiring
errno.h to be included, there is no way to access errno from a user
program, meaning we do not need to say anything about setting it as
the behaviour is not observable by a program.
That was what I had thought you meant by "not excluding". i.e. no
need to say no setting errno or modifying the floating point
environment in the normative text. I did add in a line to mention the
floating-point environment to the footnote as you suggested below.
Ah. I didn’t understand the whole intention for the “inclusive version”.
Similar to [?] regarding errno, if the <fenv.h> functions to query
flags or modify modes are not required, the implementation does not
have to maintain thread local storage for the floating-point
environment.
Regarding the [?] footnote, I don’t see that C mentions the as if rule.
Also, the C term seems to be “thread storage”. Here’s a different shot at
the footnote:
[?] Since a conforming freestanding implementation is not required to
accept program that use features in the contents of <errno.h>, the
implementation need not provide thread storage for errno. Similarly,
since a conforming freestanding implementation is not required to
accept programs that use features in the contents of <fenv.h> for
accessing floating-point exceptions or for changing the floating-point
rounding mode, the implementation need not provide thread storage for
the floating-point environment.
In 7.20 #20 we could allow freestanding implementations to define
math_errhanding to 0, to indicate that neither errno nor floating-point
exceptions are supported.
The draft footnote above doesn’t mention locales. I’m not sure what to say.
The following would be more parallel, and uses the same wording as
for math overflow and underflow in 7.12.1:
; if the integer expression math_errhandling & MATH_ERRNO is
nonzero, whether errno acquires the value ERANGE is implementation
defined; if the integer expression math_errhandling & MATH_ERREXCEPT
is nonzero, whether the "underflow" floating-point exception is
raised is implementation-defined.
Where do you see this being added? I can't see using it in
alternative 1 as that is intended to have no error handling. Was this
a proposal for alternative 2?
Yes. It’s for the underflow paragraph for alternative 2, for 7.22.1.5 and
7.29.4.1.1.
Matching the overflow paragraph to 7.12.1 gives
...; if the integer expression math_errhandling & MATH_ERRNO is
nonzero, the integer expression errno acquires the value ERANGE; if
the integer expression math_errhandling & MATH_ERREXCEPT is nonzero,
the “overflow" floating-point exception is raised.
The overflow paragraph for 7.29.4.1.1 should match 7.22.1.5.
If so, I like it as it allows implementations to avoid the exception
case as well. This however would be a change to the existing
definition which requires ERANGE for overflow. I did want to avoid
changing the existing specification too much beyond allowing
exceptions (as it seems we do for other functions).
Hmm. Isn’t it substantively the same as what you have? It makes the
floating-point numeric conversion functions like the math functions with
respect to errno and floating-point exceptions. Yes, it is a change from
the current C draft. The change is like when we added floating-point
exceptions as an alternative to errno for math.h functions.
- Jim Thomas
The (unchanged) last sentence in the last change does not match what
is in the draft.
Updated. This is probably also what Fred meant. Sorry Fred, I
misunderstood what you were referring to.
- Jim Thomas
On Jan 19, 2022, at 11:30 AM, Rajan Bhakta <rbhakta at us.ibm.com>
wrote:
(See attached file: N2823UpdateV4.html)
Regards,
Rajan Bhakta
z/OS XL C/C++ Compiler Technical Architect
ISO C Standards Representative (Canada, USA), PL22.11 Chair
C/C++ Compiler Development
rbhakta at us.ibm.com
IBM
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