Patch for Bug 26283: float.h is missing mandatory C11 fp macros like DBL_DECIMAL_DIG and LDBL_DECIMAL_DIG

[Hubert Tong via cfe-commits]

Hi Jorge,

Looks fine to me. I'll work on committing this (with minor changes) over
the weekend.
Basically, I intend to remove some extraneous parentheses and adjust the *
_EPSILON, *_MIN and *_TRUE_MIN checks to reject values equal to 0.

-- HT


On Sat, Feb 13, 2016 at 2:33 PM, Jorge Teixeira <j.lopes.teixeira at gmail.com>
wrote:

> Hubert,
>
> You're right about the *_MIN relationships, and I fixed them on the
> attached patch.
>
> As for the enums, since there we're not even testing if the literals
> are integers or fp numbers, and the Std. already reserves ranges for
> implementation-specific values for some macros, it felt more natural
> to simply test the boundary. The only exception would be
> *_HAS_SUBNORM, for which only three values are allowed. The attached
> patch implements this.
>
> Jorge
>
>
> On Sat, Feb 13, 2016 at 11:21 AM, Hubert Tong
> <hubert.reinterpretcast at gmail.com> wrote:
> > +#if ((FLT_MIN < DBL_MIN) || (DBL_MIN < LDBL_MIN))
> > +    #error "Mandatory macros {FLT,DBL,LDBL}_MIN are invalid."
> > This value again depends on the minimum exponent, and so the relationship
> > being tested here is not required to hold.
> > +#endif
> >
> > For the enumeration-like cases, perhaps it would be better to test that
> the
> > value is one of the specific values.
> >
> > -- HT
> >
> > On Fri, Feb 12, 2016 at 11:39 PM, Jorge Teixeira
> > <j.lopes.teixeira at gmail.com> wrote:
> >>
> >> Hi,
> >>
> >> I decided to strike while the iron was hot and add the remaining tests
> >> for float.h.
> >>
> >> 1) clang was missing the C11 mandatory *_HAS_SUBNORM macros, so I
> >> added them. The internal underscored versions are *_HAS_DENORM, and
> >> the Std. defines only "subnormal" and "unnormalized", so there could
> >> be, in theory, a discrepancy. I tried to learn more about APfloat
> >> supported types (IEEEsingle,PPCDoubleDouble,etc.) and how the
> >> underscored macros are generated in
> >> /lib/Preprocessor/InitPreprocessor.cpp, but it was inconclusive
> >> whether *_HAS_DENORM was added to mean subnormal like C11 expects, or
> >> not normalized. If the former, all is good, if the latter, my patch is
> >> wrong and C11 compliance is not achieved - the solution would be to
> >> study all supported fp implementations and add a new macro stating
> >> only the subnormal capabilities.
> >>
> >> 2) FLT_EVAL_METHOD was only introduced in C99, so I changed float.h
> >> and float.c to reflect that.
> >>
> >> 3) To help ensure that all macros were tested, I reordered them in
> >> float.h and float.c to match the C11 section. This added a little
> >> noise to this diff, but should be a one-off thing and simplify
> >> maintenance if further tests or new macros are added in the future.
> >>
> >> 4) The tests for the remaining macros in float.h were added. I have
> >> some reservations about the ones involving floating point literals
> >> (*_MAX, *_EPSILON, *_MIN, *_TRUE_MIN) due to the conversions and
> >> rounding among the types. Not sure how to improve them without making
> >> assumptions and/or overcomplicating the test
> >>
> >> (
> https://randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/
> ).
> >>
> >> 5) There were no meaningful fp changes in the Technical Corrigenda for
> >> C89, so the current tests (c89,c99,c11) should suffice. Not sure if
> >> gnuxx modes are affected, but I don't expect them to define
> >> __STRICT_ANSI__, so all macros should be exposed and tested
> >> successfully.
> >>
> >>
> >> Cheers,
> >>
> >> JT
> >>
> >> On Fri, Feb 12, 2016 at 2:32 PM, Hubert Tong
> >> <hubert.reinterpretcast at gmail.com> wrote:
> >> > Committed as r260710.
> >> >
> >> >
> >> > On Fri, Feb 12, 2016 at 9:53 AM, Hubert Tong
> >> > <hubert.reinterpretcast at gmail.com> wrote:
> >> >>
> >> >> Thanks Jorge. I'll work on committing this today.
> >> >>
> >> >> -- HT
> >> >>
> >> >> On Fri, Feb 12, 2016 at 12:10 AM, Jorge Teixeira
> >> >> <j.lopes.teixeira at gmail.com> wrote:
> >> >>>
> >> >>> Hubert,
> >> >>>
> >> >>> Thanks for the code review. Over the weekend I'll try to learn a bit
> >> >>> more about using Phabricator, but for now I'll reply here, and
> attach
> >> >>> a new patch.
> >> >>>
> >> >>> a) *_MANT_DIG < 1 --> *_MANT_DIG < 2
> >> >>> That is a stricter check and I agree with your rationale. Done.
> >> >>>
> >> >>> b) _MIN_EXP --> FLT_MIN_EXP
> >> >>> Done.
> >> >>>
> >> >>> c) Remove _MIN_EXP and _MIN_10_EXP FLT,DBL,LDBL comparisons
> >> >>> Yes, as you and Richard pointed out the added mantissa bits can
> >> >>> compensate for the lack of increase of the exponent.
> >> >>> Already fixed in http://reviews.llvm.org/rL260639.
> >> >>>
> >> >>> d) *_MAX_EXP and *_MIN_EXP 2,-2 --> 1,-1
> >> >>> Done.
> >> >>>
> >> >>> Richard, will do re: single patch for multiple files. Also, can you
> >> >>> close the bug report? Even if more tests for float.h get
> >> >>> added/changed, the original problem has been solved.
> >> >>>
> >> >>> JT
> >> >>>
> >> >>>
> >> >>> On Thu, Feb 11, 2016 at 8:38 PM, Hubert Tong
> >> >>> <hubert.reinterpretcast at gmail.com> wrote:
> >> >>> > Hi Jorge,
> >> >>> >
> >> >>> > I responded to the initial commit with some comments here:
> >> >>> > http://reviews.llvm.org/rL260577
> >> >>> >
> >> >>> > -- HT
> >> >>> >
> >> >>> > On Thu, Feb 11, 2016 at 7:53 PM, Jorge Teixeira
> >> >>> > <j.lopes.teixeira at gmail.com>
> >> >>> > wrote:
> >> >>> >>
> >> >>> >> > You'll also need to change <float.h> to only provide
> DECIMAL_DIG
> >> >>> >> > in
> >> >>> >> > C99
> >> >>> >> > onwards.
> >> >>> >> Done!
> >> >>> >>
> >> >>> >> > All of our -std versions are that standard plus applicable
> Defect
> >> >>> >> > Reports. So -std=c89 includes TC1 and TC2, but not Amendment 1
> >> >>> >> > (we
> >> >>> >> > have -std=c94 for that, but the only difference from our C89
> mode
> >> >>> >> > is
> >> >>> >> > the addition of digraphs).
> >> >>> >> I'll try to find the c89 TC2 and check if anything changed
> >> >>> >> regarding
> >> >>> >> these macros (unlikely).
> >> >>> >>
> >> >>> >> > __STRICT_ANSI__ is defined if Clang has not been asked to
> provide
> >> >>> >> > extensions (either GNU extensions, perhaps via a flag like
> >> >>> >> > -std=gnu99,
> >> >>> >> > or MS extensions), and is used by C library headers to
> determine
> >> >>> >> > that
> >> >>> >> > they should provide a strictly-conforming set of declarations
> >> >>> >> > without
> >> >>> >> > extensions.
> >> >>> >> Ok, so if !defined(__STRICT__ANSI__) clang should always expose
> "as
> >> >>> >> much as possible", including stuff from later versions of the
> Std.
> >> >>> >> and/or eventual extensions, just as it now on float.h and
> float.c,
> >> >>> >> right?
> >> >>> >>
> >> >>> >> > Testing __STDC_VERSION__ for C94 makes sense if you're trying
> to
> >> >>> >> > detect whether Amendment 1 features should be provided.
> >> >>> >> Since this will affect only digraphs, I guess there is no need
> (for
> >> >>> >> float.h, float.c).
> >> >>> >>
> >> >>> >> >> 3) Lastly, can you expand (...)
> >> >>> >> >
> >> >>> >> > No, it does not mean that.
> >> >>> >> >
> >> >>> >> > For PPC64, long double is (sometimes) modeled as a pair of
> >> >>> >> > doubles.
> >> >>> >> > Under that model, the smallest normalized value for long double
> >> >>> >> > is
> >> >>> >> > actually larger than the smallest normalized value for double
> >> >>> >> > (remember that for a normalized value with exponent E, all
> >> >>> >> > numbers
> >> >>> >> > of
> >> >>> >> > the form 1.XXXXX * 2^E, with the right number of mantissa
> digits,
> >> >>> >> > are
> >> >>> >> > exactly representable, so increasing the number of mantissa
> bits
> >> >>> >> > without changing the number of exponent bits increases the
> >> >>> >> > magnitude
> >> >>> >> > of the smallest normalized positive number).
> >> >>> >> >
> >> >>> >> > The set of values of long double in this model *is* a superset
> of
> >> >>> >> > the
> >> >>> >> > set of values of double.
> >> >>> >> >
> >> >>> >> I see now, and removed the bogus tests. The patch should now test
> >> >>> >> cleanly unless something needs DECIMAL_DIG but did not set the
> >> >>> >> appropriate std. level, or defined __STRICT__ANSI__.
> >> >>> >>
> >> >>> >> Thanks for the learning experience,
> >> >>> >>
> >> >>> >> JT
> >> >>> >>
> >> >>> >>
> >> >>> >>
> >> >>> >> >> From /test/Preprocessor/init.cpp:
> >> >>> >> >> // PPC64:#define __DBL_MIN_EXP__ (-1021)
> >> >>> >> >> // PPC64:#define __FLT_MIN_EXP__ (-125)
> >> >>> >> >> // PPC64:#define __LDBL_MIN_EXP__ (-968)
> >> >>> >> >>
> >> >>> >> >> This issue happened before
> >> >>> >> >>
> >> >>> >> >>
> >> >>> >> >> (
> https://lists.gnu.org/archive/html/bug-gnulib/2011-08/msg00262.html,
> >> >>> >> >> http://www.openwall.com/lists/musl/2013/11/15/1), but all it
> >> >>> >> >> means
> >> >>> >> >> is
> >> >>> >> >> that ppc64 is not compliant with C without soft-float. The
> test
> >> >>> >> >> is
> >> >>> >> >> valid and should stay, and if someone tries to compile for
> ppc64
> >> >>> >> >> in
> >> >>> >> >> c89, c99 or c11 modes, clang should 1) use soft float (bad
> >> >>> >> >> idea),
> >> >>> >> >> 2)
> >> >>> >> >> issue a diagnostic saying that that arch cannot meet the
> desired
> >> >>> >> >> C
> >> >>> >> >> standard without a big performance penalty - the diag should
> be
> >> >>> >> >> suppressible with some special cmd line argument.
> >> >>> >> >> Thus, I added the tests back and the FAIL for PPC64 for the
> time
> >> >>> >> >> being, with a comment. If you know of a way to skip only the
> >> >>> >> >> specific
> >> >>> >> >> *_MIN_EXP and *_MIN_10_EXP tests, please add it, because there
> >> >>> >> >> might
> >> >>> >> >> be more similar cases in the future.
> >> >>> >> >>
> >> >>> >> >> JT
> >> >>> >> >>
> >> >>> >> >> On Thu, Feb 11, 2016 at 3:04 PM, Richard Smith
> >> >>> >> >> <richard at metafoo.co.uk>
> >> >>> >> >> wrote:
> >> >>> >> >>> Thanks, I modified the test to also test C89 and C99 modes
> and
> >> >>> >> >>> committed this as r260577.
> >> >>> >> >>>
> >> >>> >> >>> On Thu, Feb 11, 2016 at 11:29 AM, Jorge Teixeira
> >> >>> >> >>> <j.lopes.teixeira at gmail.com> wrote:
> >> >>> >> >>>> Here is a revised test, which I renamed to
> c11-5_2_4_2_2p11.c
> >> >>> >> >>>> instead
> >> >>> >> >>>> of float.c because I am only checking a subset of what the
> >> >>> >> >>>> standard
> >> >>> >> >>>> mandates for float.h, and because there were similar
> >> >>> >> >>>> precedents,
> >> >>> >> >>>> like
> >> >>> >> >>>> test/Preprocessor/c99-*.c. Feel free to override, though.
> >> >>> >> >>>
> >> >>> >> >>> test/Preprocessor/c99-* are an aberration. The goal would be
> >> >>> >> >>> that
> >> >>> >> >>> this
> >> >>> >> >>> test grows to cover all of the parts of float.h that we
> define,
> >> >>> >> >>> so
> >> >>> >> >>> float.c seems like the appropriate name for it.
> >> >>> >> >>>
> >> >>> >> >>>> The first part checks for basic compliance with the referred
> >> >>> >> >>>> C11
> >> >>> >> >>>> paragraph, the second for internal consistency between the
> >> >>> >> >>>> underscored
> >> >>> >> >>>> and exposed versions of the macros.
> >> >>> >> >>>> No attempt was made to support C99 or C89.
> >> >>> >> >>>>
> >> >>> >> >>>> I am not very clear on the proper use of the whole lit.py /
> >> >>> >> >>>> RUN
> >> >>> >> >>>> framework, so someone should really confirm if what I wrote
> is
> >> >>> >> >>>> correct. The goal was to test both hosted and freestanding
> >> >>> >> >>>> implementations with C11, and expect no diagnostics from
> >> >>> >> >>>> either.
> >> >>> >> >>>
> >> >>> >> >>> We generally avoid testing hosted mode, because we don't want
> >> >>> >> >>> the
> >> >>> >> >>> success of our tests to depend on the libc installed on the
> >> >>> >> >>> host
> >> >>> >> >>> system.
> >> >>> >> >>>
> >> >>> >> >>>> Thanks for the help,
> >> >>> >> >>>>
> >> >>> >> >>>> JT
> >> >>> >> >>>>
> >> >>> >> >>>> On Tue, Feb 9, 2016 at 5:56 PM, Richard Smith
> >> >>> >> >>>> <richard at metafoo.co.uk>
> >> >>> >> >>>> wrote:
> >> >>> >> >>>>> On Tue, Feb 9, 2016 at 2:43 PM, Jorge Teixeira
> >> >>> >> >>>>> <j.lopes.teixeira at gmail.com> wrote:
> >> >>> >> >>>>>> Richard,
> >> >>> >> >>>>>>
> >> >>> >> >>>>>> Can you be more specific?
> >> >>> >> >>>>>>
> >> >>> >> >>>>>> I assume you mean something like my newly attached .h file
> >> >>> >> >>>>>> that
> >> >>> >> >>>>>> tests
> >> >>> >> >>>>>> very basic implementation compliance (i.e., it's required,
> >> >>> >> >>>>>> but
> >> >>> >> >>>>>> not
> >> >>> >> >>>>>> sufficient), but I would need a bit more guidance about
> the
> >> >>> >> >>>>>> structure
> >> >>> >> >>>>>> of the file, how to perform the tests, and where to
> exactly
> >> >>> >> >>>>>> place
> >> >>> >> >>>>>> and
> >> >>> >> >>>>>> name the file within test/Headers.
> >> >>> >> >>>>>>
> >> >>> >> >>>>>> I some sort of template exists, or if someone else takes
> >> >>> >> >>>>>> point
> >> >>> >> >>>>>> and
> >> >>> >> >>>>>> makes it, I can "port" the attached p11 test cases. I am
> >> >>> >> >>>>>> unsure
> >> >>> >> >>>>>> of
> >> >>> >> >>>>>> how
> >> >>> >> >>>>>> to perform a more normative compliance - for example, to
> >> >>> >> >>>>>> assert
> >> >>> >> >>>>>> that
> >> >>> >> >>>>>> LDBL_DECIMAL_DIG is 21 on x86-64 and that indeed those
> many
> >> >>> >> >>>>>> digits
> >> >>> >> >>>>>> are
> >> >>> >> >>>>>> guaranteed to be correct, etc. This is probably not
> possible
> >> >>> >> >>>>>> /
> >> >>> >> >>>>>> does
> >> >>> >> >>>>>> not make sense.
> >> >>> >> >>>>>
> >> >>> >> >>>>> That looks like a decent basic test for this. The test
> should
> >> >>> >> >>>>> be
> >> >>> >> >>>>> named
> >> >>> >> >>>>> something like test/Headers/float.c, and needs to contain a
> >> >>> >> >>>>> "RUN:"
> >> >>> >> >>>>> line so that the test runner infrastructure knows how to
> run
> >> >>> >> >>>>> it.
> >> >>> >> >>>>> You
> >> >>> >> >>>>> can look at test/Header/limits.cpp for an example of how
> this
> >> >>> >> >>>>> works.
> >> >>> >> >>>>>
> >> >>> >> >>>>> We already have platform-specific tests that
> >> >>> >> >>>>> __LDBL_DECIMAL_DIG__ is
> >> >>> >> >>>>> the right value, so you could test the values are correct
> by
> >> >>> >> >>>>> checking
> >> >>> >> >>>>> that LDBL_DECIMAL_DIG == __LDBL_DECIMAL_DIG__.
> >> >>> >> >>>>>
> >> >>> >> >>>>>> JT
> >> >>> >> >>>>>>
> >> >>> >> >>>>>> On Tue, Feb 9, 2016 at 3:58 PM, Richard Smith
> >> >>> >> >>>>>> <richard at metafoo.co.uk> wrote:
> >> >>> >> >>>>>>> Patch looks good. Please also add a testcase to
> >> >>> >> >>>>>>> test/Headers.
> >> >>> >> >>>>>>>
> >> >>> >> >>>>>>> On Tue, Feb 9, 2016 at 12:08 PM, Hubert Tong via
> >> >>> >> >>>>>>> cfe-commits
> >> >>> >> >>>>>>> <cfe-commits at lists.llvm.org> wrote:
> >> >>> >> >>>>>>>> I see no immediate issue with this patch, but I am not
> one
> >> >>> >> >>>>>>>> of
> >> >>> >> >>>>>>>> the
> >> >>> >> >>>>>>>> usual
> >> >>> >> >>>>>>>> reviewers for this part of the code base.
> >> >>> >> >>>>>>>>
> >> >>> >> >>>>>>>> -- HT
> >> >>> >> >>>>>>>>
> >> >>> >> >>>>>>>>
> >> >>> >> >>>>>>>> On Tue, Feb 9, 2016 at 2:56 PM, Jorge Teixeira
> >> >>> >> >>>>>>>> <j.lopes.teixeira at gmail.com>
> >> >>> >> >>>>>>>> wrote:
> >> >>> >> >>>>>>>>>
> >> >>> >> >>>>>>>>> Thanks Hubert. Somehow I omitted that prefix when
> typing
> >> >>> >> >>>>>>>>> the
> >> >>> >> >>>>>>>>> macros,
> >> >>> >> >>>>>>>>> and I did not noticed it when I was testing because on
> my
> >> >>> >> >>>>>>>>> arch
> >> >>> >> >>>>>>>>> DECIMAL_DIG is defined to be the LDBL version...
> >> >>> >> >>>>>>>>>
> >> >>> >> >>>>>>>>> Updated patch is attached.
> >> >>> >> >>>>>>>>>
> >> >>> >> >>>>>>>>> JT
> >> >>> >> >>>>>>>>>
> >> >>> >> >>>>>>>>> On Tue, Feb 9, 2016 at 1:41 PM, Hubert Tong
> >> >>> >> >>>>>>>>> <hubert.reinterpretcast at gmail.com> wrote:
> >> >>> >> >>>>>>>>> > There is a __LDBL_DECIMAL_DIG__ predefined macro.
> >> >>> >> >>>>>>>>> > __DECIMAL_DIG__ will
> >> >>> >> >>>>>>>>> > not
> >> >>> >> >>>>>>>>> > always be the same as __LDBL_DECIMAL_DIG__.
> >> >>> >> >>>>>>>>> >
> >> >>> >> >>>>>>>>> > -- HT
> >> >>> >> >>>>>>>>> >
> >> >>> >> >>>>>>>>> > On Mon, Feb 8, 2016 at 11:26 PM, Jorge Teixeira via
> >> >>> >> >>>>>>>>> > cfe-commits
> >> >>> >> >>>>>>>>> > <cfe-commits at lists.llvm.org> wrote:
> >> >>> >> >>>>>>>>> >>
> >> >>> >> >>>>>>>>> >> Hi, I filed the bug
> >> >>> >> >>>>>>>>> >> (https://llvm.org/bugs/show_bug.cgi?id=26283) some
> >> >>> >> >>>>>>>>> >> time ago and nobody picked it up, so here is a
> trivial
> >> >>> >> >>>>>>>>> >> patch
> >> >>> >> >>>>>>>>> >> exposing
> >> >>> >> >>>>>>>>> >> the missing macros, that to the best of my ability
> >> >>> >> >>>>>>>>> >> were
> >> >>> >> >>>>>>>>> >> already
> >> >>> >> >>>>>>>>> >> present as the internal underscored versions.
> >> >>> >> >>>>>>>>> >>
> >> >>> >> >>>>>>>>> >> Perhaps a more general bug about C11 floating point
> >> >>> >> >>>>>>>>> >> (lack
> >> >>> >> >>>>>>>>> >> of)
> >> >>> >> >>>>>>>>> >> conformance should be filed, so that some form of
> unit
> >> >>> >> >>>>>>>>> >> test/macro
> >> >>> >> >>>>>>>>> >> validation could be worked on, but this patch does
> >> >>> >> >>>>>>>>> >> scratch my
> >> >>> >> >>>>>>>>> >> current
> >> >>> >> >>>>>>>>> >> itch.
> >> >>> >> >>>>>>>>> >>
> >> >>> >> >>>>>>>>> >> Successfully tested on x86-64 Xubuntu 14.04 with
> clang
> >> >>> >> >>>>>>>>> >> 3.8
> >> >>> >> >>>>>>>>> >> from the
> >> >>> >> >>>>>>>>> >> ppa, patched with the attached diff.
> >> >>> >> >>>>>>>>> >>
> >> >>> >> >>>>>>>>> >> First contribution, so feel free to suggest
> >> >>> >> >>>>>>>>> >> improvements
> >> >>> >> >>>>>>>>> >> or
> >> >>> >> >>>>>>>>> >> point to
> >> >>> >> >>>>>>>>> >> more detailed step-by-step instructions/guidelines.
> >> >>> >> >>>>>>>>> >>
> >> >>> >> >>>>>>>>> >> Cheers,
> >> >>> >> >>>>>>>>> >>
> >> >>> >> >>>>>>>>> >> JT
> >> >>> >> >>>>>>>>> >>
> >> >>> >> >>>>>>>>> >> _______________________________________________
> >> >>> >> >>>>>>>>> >> cfe-commits mailing list
> >> >>> >> >>>>>>>>> >> cfe-commits at lists.llvm.org
> >> >>> >> >>>>>>>>> >>
> >> >>> >> >>>>>>>>> >>
> >> >>> >> >>>>>>>>> >>
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
> >> >>> >> >>>>>>>>> >>
> >> >>> >> >>>>>>>>> >
> >> >>> >> >>>>>>>>
> >> >>> >> >>>>>>>>
> >> >>> >> >>>>>>>>
> >> >>> >> >>>>>>>> _______________________________________________
> >> >>> >> >>>>>>>> cfe-commits mailing list
> >> >>> >> >>>>>>>> cfe-commits at lists.llvm.org
> >> >>> >> >>>>>>>>
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
> >> >>> >> >>>>>>>>
> >> >>> >
> >> >>> >
> >> >>
> >> >>
> >> >
> >
> >
>
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