[libcxx-commits] [libcxx] 4608df5 - [libc++] Simplify __bitset::__init (#121357)
via libcxx-commits
libcxx-commits at lists.llvm.org
Wed May 28 09:09:54 PDT 2025
Author: Peng Liu
Date: 2025-05-28T12:09:50-04:00
New Revision: 4608df5b9fea7322714fc5fe7e6bcc5e5e3a666a
URL: https://github.com/llvm/llvm-project/commit/4608df5b9fea7322714fc5fe7e6bcc5e5e3a666a
DIFF: https://github.com/llvm/llvm-project/commit/4608df5b9fea7322714fc5fe7e6bcc5e5e3a666a.diff
LOG: [libc++] Simplify __bitset::__init (#121357)
This PR simplifies `__bitset::__init` into a more compact and readable
form, which avoids redundant computations of a `size_t` value and
eliminates the overhead of a local array.
Added:
Modified:
libcxx/include/bitset
libcxx/test/benchmarks/bitset.bench.cpp
Removed:
################################################################################
diff --git a/libcxx/include/bitset b/libcxx/include/bitset
index eee5a51a39e24..13ad31f5f924f 100644
--- a/libcxx/include/bitset
+++ b/libcxx/include/bitset
@@ -273,26 +273,16 @@ inline _LIBCPP_CONSTEXPR __bitset<_N_words, _Size>::__bitset() _NOEXCEPT
template <size_t _N_words, size_t _Size>
void __bitset<_N_words, _Size>::__init(unsigned long long __v, false_type) _NOEXCEPT {
- __storage_type __t[sizeof(unsigned long long) / sizeof(__storage_type)];
- size_t __sz = _Size;
- for (size_t __i = 0; __i < sizeof(__t) / sizeof(__t[0]); ++__i, __v >>= __bits_per_word, __sz -= __bits_per_word)
- if (__sz < __bits_per_word)
- __t[__i] = static_cast<__storage_type>(__v) & (1ULL << __sz) - 1;
- else
- __t[__i] = static_cast<__storage_type>(__v);
-
- std::copy(__t, __t + sizeof(__t) / sizeof(__t[0]), __first_);
- std::fill(
- __first_ + sizeof(__t) / sizeof(__t[0]), __first_ + sizeof(__first_) / sizeof(__first_[0]), __storage_type(0));
+ const size_t __n_words = std::min((sizeof(unsigned long long) - 1) / sizeof(__storage_type) + 1, _N_words);
+ for (size_t __i = 0; __i < __n_words; ++__i, __v >>= __bits_per_word)
+ __first_[__i] = static_cast<__storage_type>(__v);
+ std::fill(__first_ + __n_words, __first_ + _N_words, __storage_type(0));
}
template <size_t _N_words, size_t _Size>
inline _LIBCPP_HIDE_FROM_ABI void __bitset<_N_words, _Size>::__init(unsigned long long __v, true_type) _NOEXCEPT {
__first_[0] = __v;
- if (_Size < __bits_per_word)
- __first_[0] &= (1ULL << _Size) - 1;
-
- std::fill(__first_ + 1, __first_ + sizeof(__first_) / sizeof(__first_[0]), __storage_type(0));
+ std::fill(__first_ + 1, __first_ + _N_words, __storage_type(0));
}
# endif // _LIBCPP_CXX03_LANG
@@ -314,7 +304,7 @@ inline _LIBCPP_CONSTEXPR __bitset<_N_words, _Size>::__bitset(unsigned long long
# endif
{
# ifdef _LIBCPP_CXX03_LANG
- __init(__v, integral_constant<bool, sizeof(unsigned long long) == sizeof(__storage_type)>());
+ __init(__v, integral_constant<bool, sizeof(unsigned long long) <= sizeof(__storage_type)>());
# endif
}
@@ -658,7 +648,8 @@ public:
// 23.3.5.1 constructors:
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bitset() _NOEXCEPT {}
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bitset(unsigned long long __v) _NOEXCEPT : __base(__v) {}
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bitset(unsigned long long __v) _NOEXCEPT
+ : __base(sizeof(unsigned long long) * CHAR_BIT <= _Size ? __v : __v & ((1ULL << _Size) - 1)) {}
template <class _CharT, __enable_if_t<_IsCharLikeType<_CharT>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 explicit bitset(
const _CharT* __str,
diff --git a/libcxx/test/benchmarks/bitset.bench.cpp b/libcxx/test/benchmarks/bitset.bench.cpp
index 5e95d3aad1cb2..8fcf52e9425ce 100644
--- a/libcxx/test/benchmarks/bitset.bench.cpp
+++ b/libcxx/test/benchmarks/bitset.bench.cpp
@@ -103,4 +103,14 @@ BENCHMARK(BM_BitsetToString<262144>)->Arg(50)->Name("BM_BitsetToString<262144>/U
BENCHMARK(BM_BitsetToString<524288>)->Arg(50)->Name("BM_BitsetToString<524288>/Uniform (50%)");
BENCHMARK(BM_BitsetToString<1048576>)->Arg(50)->Name("BM_BitsetToString<1048576>/Uniform (50%)"); // 1 << 20
+static void BM_ctor_ull(benchmark::State& state) {
+ unsigned long long val = (1ULL << state.range(0)) - 1;
+ for (auto _ : state) {
+ std::bitset<128> b(val);
+ benchmark::DoNotOptimize(b);
+ }
+}
+
+BENCHMARK(BM_ctor_ull)->DenseRange(1, 63);
+
BENCHMARK_MAIN();
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