[libcxx-commits] [libcxx] [libc++] Improve bitset::to_ullong Implementation (PR #121348)

[Peng Liu via libcxx-commits]

https://github.com/winner245 updated https://github.com/llvm/llvm-project/pull/121348

>From 5751c13e2c84b828a54bf62b2af86fde3ebb705a Mon Sep 17 00:00:00 2001
From: Peng Liu <winner245 at hotmail.com>
Date: Mon, 30 Dec 2024 12:19:19 -0500
Subject: [PATCH] Improve bitset::to_ullong Implementation

---
 libcxx/include/bitset | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/libcxx/include/bitset b/libcxx/include/bitset
index 919d2a0f07e096..2f2129bb8cc767 100644
--- a/libcxx/include/bitset
+++ b/libcxx/include/bitset
@@ -133,6 +133,7 @@ template <size_t N> struct hash<std::bitset<N>>;
 #  include <__algorithm/fill.h>
 #  include <__algorithm/fill_n.h>
 #  include <__algorithm/find.h>
+#  include <__algorithm/min.h>
 #  include <__assert>
 #  include <__bit_reference>
 #  include <__config>
@@ -381,8 +382,9 @@ __bitset<_N_words, _Size>::to_ullong(true_type, true_type) const {
   unsigned long long __r = __first_[0];
   _LIBCPP_DIAGNOSTIC_PUSH
   _LIBCPP_GCC_DIAGNOSTIC_IGNORED("-Wshift-count-overflow")
-  for (size_t __i = 1; __i < sizeof(unsigned long long) / sizeof(__storage_type); ++__i)
-    __r |= static_cast<unsigned long long>(__first_[__i]) << (sizeof(__storage_type) * CHAR_BIT);
+  size_t __n_words = std::min<size_t>(_N_words, sizeof(unsigned long long) / sizeof(__storage_type));
+  for (size_t __i = 1; __i < __n_words; ++__i)
+    __r |= static_cast<unsigned long long>(__first_[__i]) << (sizeof(__storage_type) * CHAR_BIT * __i);
   _LIBCPP_DIAGNOSTIC_POP
   return __r;
 }