[libcxx-commits] [libcxx] [libc++] Conditionally declare `lgamma_r` as noexcept (PR #156547)

[Yuxuan Chen via libcxx-commits]

https://github.com/yuxuanchen1997 updated https://github.com/llvm/llvm-project/pull/156547

>From ae1da16275176f204f693ec7638a9250cf5115cd Mon Sep 17 00:00:00 2001
From: Yuxuan Chen <ych at meta.com>
Date: Tue, 2 Sep 2025 15:03:56 -0700
Subject: [PATCH] [libc++] Conditionally declarelgamma_r as noexcept

---
 libcxx/include/__random/binomial_distribution.h | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/libcxx/include/__random/binomial_distribution.h b/libcxx/include/__random/binomial_distribution.h
index b4b4340827761..17a2e802e134e 100644
--- a/libcxx/include/__random/binomial_distribution.h
+++ b/libcxx/include/__random/binomial_distribution.h
@@ -97,13 +97,19 @@ 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 _LIBCPP_GLIBC_PREREQ(2, 8) || 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;