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[libc++] Conditionally declare lgamma_r as noexcept #156547

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merged 1 commit into from
Sep 8, 2025
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[libc++] Conditionally declare lgamma_r as noexcept #156547

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18 changes: 14 additions & 4 deletions libcxx/include/__random/binomial_distribution.h
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Original file line number Diff line number Diff line change
Expand Up @@ -97,13 +97,23 @@ class binomial_distribution {
}
};

// The LLVM C library provides this with conflicting `noexcept` attributes.
#if !defined(_LIBCPP_MSVCRT_LIKE) && !defined(__LLVM_LIBC__)
extern "C" double lgamma_r(double, int*);
// Some libc declares the math functions to be `noexcept`.
#if defined(_LIBCPP_GLIBC_PREREQ)
# if _LIBCPP_GLIBC_PREREQ(2, 8)
# define _LIBCPP_LGAMMA_R_NOEXCEPT _NOEXCEPT
# endif
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Does this need an #else? Else the macro isn't defined if the inner #if here isn't true, right?

We're getting this on our bots, I'm guessing due to this:

[187/130551] CXX android_clang_arm/obj/third_party/abseil-cpp/absl/strings/cordz_functions/cordz_functions.o
../../third_party/llvm-build/Release+Asserts/bin/clang++ -MMD -MF android_clang_arm/obj/third_party/abseil-cpp/absl/strings/cordz_functions/co...(too long)
In file included from ../../third_party/abseil-cpp/absl/strings/internal/cordz_functions.cc:20:
In file included from ../../third_party/libc++/src/include/random:1685:
../../third_party/libc++/src/include/__random/binomial_distribution.h:112:42: error: expected function body after function declarator
  112 | extern "C" double lgamma_r(double, int*) _LIBCPP_LGAMMA_R_NOEXCEPT;
      |                                          ^
1 error generated.

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@jhuber6 jhuber6 Sep 9, 2025 •
edited
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Same thing I'm seeing

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#157610 added it. Thanks!

#elif defined(__LLVM_LIBC__)
# define _LIBCPP_LGAMMA_R_NOEXCEPT _NOEXCEPT
#else
# define _LIBCPP_LGAMMA_R_NOEXCEPT
#endif

#if !defined(_LIBCPP_MSVCRT_LIKE)
extern "C" double lgamma_r(double, int*) _LIBCPP_LGAMMA_R_NOEXCEPT;
#endif

inline _LIBCPP_HIDE_FROM_ABI double __libcpp_lgamma(double __d) {
#if defined(_LIBCPP_MSVCRT_LIKE) || defined(__LLVM_LIBC__)
#if defined(_LIBCPP_MSVCRT_LIKE)
return lgamma(__d);
#else
int __sign;
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