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

Thu Feb 11 17:38:59 PST 2016

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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