[Bug math/19439] Unix98 isinf and isnan functions conflict with C++11

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https://sourceware.org/bugzilla/show_bug.cgi?id=19439

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=d9b965fa56350d6eea9f7f438a0714c7ffbb183f

commit d9b965fa56350d6eea9f7f438a0714c7ffbb183f
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Mon Jan 11 13:34:52 2016 -0200

    Fix isinf/isnan declaration conflict with C++11

    GLIBC declares isinf and isnan as expected by Unix98 and for C99 programs
    these functions are hidden by the generics inf and isnan macros.
    However C++11 defines isinf and isnan with the same semantics as C99
    but requires that they are functions not macros (C++11 26.8 [c.math]
    paragraph 10).

    This then results in a conflict for perfectly valid C++11 programs:

    --
    using std::isinf;
    using std::isnan;

    double d1 = isinf(1.0);
    double d2 = isnan(1.0);

    d.cc:3:12: error: âconstexpr bool std::isinf(double)â conflicts with a
previous declaration
     using std::isinf;
    [...]
    /usr/include/bits/mathcalls.h:201:1: note: previous declaration âint
isinf(double)â
     __MATHDECL_1 (int,isinf,, (_Mdouble_ __value)) __attribute__
((__const__));
    [...]
    --

    This patch fixes the prototypes by leaving the obsolete functions
    defined for C++98 code (since they do not conflict with any standard
    function in C++98), however preventing them on C++11.

    No issues found in libstdc++ tests and check on x86_64 and i686 with
    glibc testsuite.

    Patch from Jonathan Wakely  <jwakely.gcc@gmail.com>.

        [BZ #19439]
        * math/bits/mathcalls.h
        [!__cplusplus || __cplusplus < 201103L] (isinf): Do not declare
        prototype.
        [!__cplusplus || __cplusplus < 201103L] (isnan): Likewise.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog             |    9 +++++++++
 math/bits/mathcalls.h |    4 ++++
 2 files changed, 13 insertions(+), 0 deletions(-)

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