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 cfe-commits at lists.llvm.org
Fri Feb 12 06:53:18 PST 2016 

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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