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Subject: Re: [PATCH] Define iszero as a function template for C++ [BZ #20715]
To: Joseph Myers <joseph@codesourcery.com>
References: <2b2fa3c4-5bd6-4025-717f-fe2e2ee19555@redhat.com>
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Cc: GNU C Library <libc-alpha@sourceware.org>
From: Florian Weimer <fweimer@redhat.com>
Message-ID: <c838d4f1-99fa-6736-532e-1db62d5d5ff8@redhat.com>
Date: Sat, 22 Oct 2016 15:35:00 -0000
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On 10/21/2016 06:31 PM, Florian Weimer wrote:
> On 10/21/2016 06:23 PM, Joseph Myers wrote:
>> On Fri, 21 Oct 2016, Florian Weimer wrote:
>>
>>> On 10/21/2016 06:12 PM, Joseph Myers wrote:
>>>> On Fri, 21 Oct 2016, Florian Weimer wrote:
>>>>
>>>>> Tested on x86_64, ppc64, ppc64le, s390x, aarch64.
>>>>>
>>>>> I'm not sure if the new test is particularly meaningful, but at
>>>>> least it
>>>>> catches syntax errors in <math.h>.
>>>>
>>>> This seems fine to me (with negative zero included in the testcase),
>>>
>>> Oh.  How do I get a negative zero?  Would T{-0.0} be sufficient?  Or
>>> should I
>>
>> Yes, T{-0.0} or -T{0} should suffice.
>
> Thanks.  Here is what I've committed.  Everything is optimized away
> anyway (but I deliberately introduced a bug to make sure the test still
> tests something).

I had to commit the attached follow-on fix to make

extern "C" {
#include <math.h>
}

work again.

Florian


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math.h: Wrap C++ bits in extern "C++"

It is still common to include system header files in an extern "C"
block.  This means that exiting <math.h>'s own extern "C" block
is not sufficient to get back to C++ mode.  Use an extern "C++"
wrapper instead.

2016-10-22  Florian Weimer  <fweimer@redhat.com>

	* math/math.h [__cplusplus] (iszero): Wrap C++ bits in extern
	"C++", to override a potential extern "C" directive around the
	header file inclusion.

diff --git a/math/math.h b/math/math.h
index 0220d08..7c0c709 100644
--- a/math/math.h
+++ b/math/math.h
@@ -342,7 +342,7 @@ enum
 #   define iszero(x) (((__typeof (x)) (x)) == 0)
 #  endif
 # else	/* __cplusplus */
-__END_DECLS
+extern "C++" {
 template <class __T> inline bool
 iszero (__T __val)
 {
@@ -352,7 +352,7 @@ iszero (__T __val)
   return __val == 0;
 #  endif
 }
-__BEGIN_DECLS
+} /* extern C++ */
 # endif	/* __cplusplus */
 #endif /* Use IEC_60559_BFP_EXT.  */
 

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