Vectorize bitset from string construction

benchmarks/CMakeLists.txt

@@ -108,6 +108,7 @@ function(add_benchmark name)
     target_compile_definitions(benchmark-${name} PRIVATE BENCHMARK_STATIC_DEFINE)
 endfunction()
 
+add_benchmark(bitset_from_string src/bitset_from_string.cpp)
 add_benchmark(bitset_to_string src/bitset_to_string.cpp)
 add_benchmark(find_and_count src/find_and_count.cpp)
 add_benchmark(find_first_of src/find_first_of.cpp)

benchmarks/src/bitset_from_string.cpp

@@ -0,0 +1,93 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <array>
+#include <benchmark/benchmark.h>
+#include <bitset>
+#include <climits>
+#include <cstddef>
+#include <cstdint>
+#include <cstdlib>
+#include <random>
+
+using namespace std;
+
+namespace {
+    template <typename charT, size_t Min_length, size_t N>
+    const auto random_digits_init() {
+        mt19937_64 rnd{};
+        uniform_int_distribution<> dis('0', '1');
+        std::basic_string<charT> str;
+
+        constexpr size_t number_of_bitsets = (Min_length + N - 1) / N;
+        static_assert(number_of_bitsets != 0);
+
+        constexpr size_t actual_size = number_of_bitsets * (N + 1); // +1 for \0
+
+        std::array<charT, actual_size> result;
+
+        for (auto dest = result.begin(); dest != result.end();) {
+            for (size_t i = 0; i != N; ++i, ++dest) {
+                *dest = static_cast<charT>(dis(rnd));
+            }
+
+            *dest = charT{'\0'};
+            ++dest;
+        }
+
+        return result;
+    }
+
+    enum class length_type : bool { char_count, null_term };
+
+    template <size_t N, typename charT>
+    const auto random_digits = random_digits_init<charT, 2048, N>();
+
+    template <length_type Length, size_t N, class charT>
+    void BM_bitset_from_string(benchmark::State& state) {
+        const auto& bit_string = random_digits<N, charT>;
+        for (auto _ : state) {
+            benchmark::DoNotOptimize(bit_string);
+            const charT* const data = bit_string.data();
+            for (size_t pos = 0, max = bit_string.size(); pos != max; pos += N + 1) {
+                if constexpr (Length == length_type::char_count) {
+                    bitset<N> bs(data + pos, N);
+                    benchmark::DoNotOptimize(bs);
+                } else {
+                    bitset<N> bs(data + pos);
+                    benchmark::DoNotOptimize(bs);
+                }
+            }
+        }
+    }
+} // namespace
+
+BENCHMARK(BM_bitset_from_string<length_type::char_count, 15, char>);
+BENCHMARK(BM_bitset_from_string<length_type::char_count, 16, char>);
+BENCHMARK(BM_bitset_from_string<length_type::char_count, 36, char>);
+BENCHMARK(BM_bitset_from_string<length_type::char_count, 64, char>);
+BENCHMARK(BM_bitset_from_string<length_type::char_count, 512, char>);
+BENCHMARK(BM_bitset_from_string<length_type::char_count, 2048, char>);
+
+BENCHMARK(BM_bitset_from_string<length_type::char_count, 15, wchar_t>);
+BENCHMARK(BM_bitset_from_string<length_type::char_count, 16, wchar_t>);
+BENCHMARK(BM_bitset_from_string<length_type::char_count, 36, wchar_t>);
+BENCHMARK(BM_bitset_from_string<length_type::char_count, 64, wchar_t>);
+BENCHMARK(BM_bitset_from_string<length_type::char_count, 512, wchar_t>);
+BENCHMARK(BM_bitset_from_string<length_type::char_count, 2048, wchar_t>);
+
+BENCHMARK(BM_bitset_from_string<length_type::null_term, 15, char>);
+BENCHMARK(BM_bitset_from_string<length_type::null_term, 16, char>);
+BENCHMARK(BM_bitset_from_string<length_type::null_term, 36, char>);
+BENCHMARK(BM_bitset_from_string<length_type::null_term, 64, char>);
+BENCHMARK(BM_bitset_from_string<length_type::null_term, 512, char>);
+BENCHMARK(BM_bitset_from_string<length_type::null_term, 2048, char>);
+
+BENCHMARK(BM_bitset_from_string<length_type::null_term, 15, wchar_t>);
+BENCHMARK(BM_bitset_from_string<length_type::null_term, 16, wchar_t>);
+BENCHMARK(BM_bitset_from_string<length_type::null_term, 36, wchar_t>);
+BENCHMARK(BM_bitset_from_string<length_type::null_term, 64, wchar_t>);
+BENCHMARK(BM_bitset_from_string<length_type::null_term, 512, wchar_t>);
+BENCHMARK(BM_bitset_from_string<length_type::null_term, 2048, wchar_t>);
+
+BENCHMARK_MAIN();

stl/inc/bitset

@@ -23,11 +23,19 @@ _STL_DISABLE_CLANG_WARNINGS
 #endif // !defined(_STD_BITSET_TO_STREAM_STACK_RESERVATION)
 
 #if _USE_STD_VECTOR_ALGORITHMS
+// These bitset functions sometimes assume bit array has zero padding to multiple of 2 or 4 bytes
+// The assumptions hold true even for vNext suggestion to use smaller types for small bitsets
+// due to vectorization thresholds.
+
 extern "C" {
 __declspec(noalias) void __stdcall __std_bitset_to_string_1(
     char* _Dest, const void* _Src, size_t _Size_bits, char _Elem0, char _Elem1) noexcept;
 __declspec(noalias) void __stdcall __std_bitset_to_string_2(
     wchar_t* _Dest, const void* _Src, size_t _Size_bits, wchar_t _Elem0, wchar_t _Elem1) noexcept;
+__declspec(noalias) bool __stdcall __std_bitset_from_string_1(void* _Dest, const char* _Src, size_t _Size_bytes,
+    size_t _Size_bits, size_t _Size_chars, char _Elem0, char _Elem1) noexcept;
+__declspec(noalias) bool __stdcall __std_bitset_from_string_2(void* _Dest, const wchar_t* _Src, size_t _Size_bytes,
+    size_t _Size_bits, size_t _Size_chars, wchar_t _Elem0, wchar_t _Elem1) noexcept;
 } // extern "C"
 #endif // _USE_STD_VECTOR_ALGORITHMS
 
@@ -115,6 +123,30 @@ public:
 private:
     template <class _Traits, class _Elem>
     _CONSTEXPR23 void _Construct(const _Elem* const _Ptr, size_t _Count, const _Elem _Elem0, const _Elem _Elem1) {
+#if _USE_STD_VECTOR_ALGORITHMS
+        constexpr size_t _Bitset_from_string_vector_threshold = 16;
+        if constexpr (_Bits >= _Bitset_from_string_vector_threshold
+                      && _Is_specialization_v<_Traits, char_traits> && sizeof(_Elem) <= 2) {
+            if (!_STD _Is_constant_evaluated()) {
+                bool _Result;
+
+                if constexpr (sizeof(_Elem) == 1) {
+                    _Result = __std_bitset_from_string_1(_Array, reinterpret_cast<const char*>(_Ptr), sizeof(_Array),
+                        _Bits, _Count, static_cast<char>(_Elem0), static_cast<char>(_Elem1));
+                } else {
+                    _STL_INTERNAL_STATIC_ASSERT(sizeof(_Elem) == 2);
+                    _Result = __std_bitset_from_string_2(_Array, reinterpret_cast<const wchar_t*>(_Ptr), sizeof(_Array),
+                        _Bits, _Count, static_cast<wchar_t>(_Elem0), static_cast<wchar_t>(_Elem1));
+                }
+
+                if (!_Result) {
+                    _Xinv();
+                }
+
+                return;
+            }
+        }
+#endif // _USE_STD_VECTOR_ALGORITHMS
         if (_Count > _Bits) {
             for (size_t _Idx = _Bits; _Idx < _Count; ++_Idx) {
                 const auto _Ch = _Ptr[_Idx];
@@ -462,8 +494,8 @@ public:
     _CONSTEXPR23 void _To_string(
         _Elem* const _Buf, const size_t _Len, const _Elem _Elem0, const _Elem _Elem1) const noexcept {
 #if _USE_STD_VECTOR_ALGORITHMS
-        constexpr size_t _Bitset_vector_threshold = 32;
-        if constexpr (_Bits >= _Bitset_vector_threshold && is_integral_v<_Elem> && sizeof(_Elem) <= 2) {
+        constexpr size_t _Bitset_to_string_vector_threshold = 32;
+        if constexpr (_Bits >= _Bitset_to_string_vector_threshold && is_integral_v<_Elem> && sizeof(_Elem) <= 2) {
             if (!_Is_constant_evaluated()) {
                 if constexpr (sizeof(_Elem) == 1) {
                     __std_bitset_to_string_1(reinterpret_cast<char*>(_Buf), _Array, _Len, static_cast<char>(_Elem0),