bkietz commented on a change in pull request #10915: URL: https://github.com/apache/arrow/pull/10915#discussion_r687694889
########## File path: cpp/src/arrow/util/small_vector.h ########## @@ -0,0 +1,509 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +#pragma once + +#include <algorithm> +#include <cassert> +#include <cstddef> +#include <initializer_list> +#include <limits> +#include <new> +#include <type_traits> +#include <utility> + +#include "arrow/util/macros.h" + +namespace arrow { +namespace internal { + +#if __cplusplus >= 201703L +using std::launder; +#else +// TODO factor out from result.h + +// template <class T> +// constexpr T* launder(T* p) noexcept { +// return p; +// } +#endif + +template <typename ValueType, typename PointerType, typename ReferenceType> +class VectorIterator { + public: + using value_type = ValueType; + using pointer = PointerType; + using reference = ReferenceType; + using difference_type = ptrdiff_t; + using iterator_category = std::random_access_iterator_tag; + + // Some algorithms need to default-construct an iterator + constexpr VectorIterator() noexcept = default; + + constexpr explicit VectorIterator(pointer ptr) noexcept : ptr_(ptr) {} + + // Value access + constexpr reference operator*() const { return *ptr_; } + + constexpr reference operator[](difference_type n) const { return ptr_[n]; } + + // Forward / backward + VectorIterator& operator++() { + ++ptr_; + return *this; + } + VectorIterator& operator--() { + --ptr_; + return *this; + } + VectorIterator operator++(int) { + VectorIterator tmp(*this); + ++ptr_; + return tmp; + } + VectorIterator operator--(int) { + VectorIterator tmp(*this); + --ptr_; + return tmp; + } + + // Arithmetic + constexpr difference_type operator-(const VectorIterator& other) const { + return ptr_ - other.ptr_; + } + constexpr VectorIterator operator+(difference_type n) const { + return VectorIterator(ptr_ + n); + } + constexpr VectorIterator operator-(difference_type n) const { + return VectorIterator(ptr_ - n); + } + VectorIterator& operator+=(difference_type n) { + ptr_ += n; + return *this; + } + VectorIterator& operator-=(difference_type n) { + ptr_ -= n; + return *this; + } + + // Comparisons + constexpr bool operator==(const VectorIterator& other) const { + return ptr_ == other.ptr_; + } + constexpr bool operator!=(const VectorIterator& other) const { + return ptr_ != other.ptr_; + } + constexpr bool operator<(const VectorIterator& other) const { + return ptr_ < other.ptr_; + } + constexpr bool operator>(const VectorIterator& other) const { + return ptr_ > other.ptr_; + } + constexpr bool operator<=(const VectorIterator& other) const { + return ptr_ <= other.ptr_; + } + constexpr bool operator>=(const VectorIterator& other) const { + return ptr_ >= other.ptr_; + } + + private: + pointer ptr_ = NULLPTR; +}; + +template <typename T> +class StaticVectorMixin { + protected: + // properly aligned uninitialized storage for N T's + using storage_type = typename std::aligned_storage<sizeof(T), alignof(T)>::type; + + static T* ptr_at(storage_type* p, size_t i) { + return launder(reinterpret_cast<T*>(&p[i])); + } + + static const T* ptr_at(const storage_type* p, size_t i) { + return launder(reinterpret_cast<const T*>(&p[i])); + } + + static void move_storage(storage_type* src, storage_type* dest, size_t n) { + for (size_t i = 0; i < n; ++i) { + T* src_item = ptr_at(src, i); + T* dest_item = ptr_at(dest, i); + new (dest_item) T(std::move(*src_item)); + src_item->~T(); + } + } + + static void destroy_storage(storage_type* p, size_t n) { + for (size_t i = 0; i < n; ++i) { + ptr_at(p, i)->~T(); + } + } +}; + +template <typename T, size_t N, bool NonTrivialDestructor> +class StaticVectorBaseStorage : public StaticVectorMixin<T> { Review comment: Could we avoid inheritance here? ########## File path: cpp/src/arrow/util/small_vector.h ########## @@ -0,0 +1,509 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +#pragma once + +#include <algorithm> +#include <cassert> +#include <cstddef> +#include <initializer_list> +#include <limits> +#include <new> +#include <type_traits> +#include <utility> + +#include "arrow/util/macros.h" + +namespace arrow { +namespace internal { + +#if __cplusplus >= 201703L +using std::launder; +#else +// TODO factor out from result.h + +// template <class T> +// constexpr T* launder(T* p) noexcept { +// return p; +// } +#endif + +template <typename ValueType, typename PointerType, typename ReferenceType> +class VectorIterator { + public: + using value_type = ValueType; + using pointer = PointerType; + using reference = ReferenceType; + using difference_type = ptrdiff_t; + using iterator_category = std::random_access_iterator_tag; + + // Some algorithms need to default-construct an iterator + constexpr VectorIterator() noexcept = default; + + constexpr explicit VectorIterator(pointer ptr) noexcept : ptr_(ptr) {} + + // Value access + constexpr reference operator*() const { return *ptr_; } + + constexpr reference operator[](difference_type n) const { return ptr_[n]; } + + // Forward / backward + VectorIterator& operator++() { + ++ptr_; + return *this; + } + VectorIterator& operator--() { + --ptr_; + return *this; + } + VectorIterator operator++(int) { + VectorIterator tmp(*this); + ++ptr_; + return tmp; + } + VectorIterator operator--(int) { + VectorIterator tmp(*this); + --ptr_; + return tmp; + } + + // Arithmetic + constexpr difference_type operator-(const VectorIterator& other) const { + return ptr_ - other.ptr_; + } + constexpr VectorIterator operator+(difference_type n) const { + return VectorIterator(ptr_ + n); + } + constexpr VectorIterator operator-(difference_type n) const { + return VectorIterator(ptr_ - n); + } + VectorIterator& operator+=(difference_type n) { + ptr_ += n; + return *this; + } + VectorIterator& operator-=(difference_type n) { + ptr_ -= n; + return *this; + } + + // Comparisons + constexpr bool operator==(const VectorIterator& other) const { + return ptr_ == other.ptr_; + } + constexpr bool operator!=(const VectorIterator& other) const { + return ptr_ != other.ptr_; + } + constexpr bool operator<(const VectorIterator& other) const { + return ptr_ < other.ptr_; + } + constexpr bool operator>(const VectorIterator& other) const { + return ptr_ > other.ptr_; + } + constexpr bool operator<=(const VectorIterator& other) const { + return ptr_ <= other.ptr_; + } + constexpr bool operator>=(const VectorIterator& other) const { + return ptr_ >= other.ptr_; + } + + private: + pointer ptr_ = NULLPTR; +}; + +template <typename T> +class StaticVectorMixin { + protected: + // properly aligned uninitialized storage for N T's + using storage_type = typename std::aligned_storage<sizeof(T), alignof(T)>::type; + + static T* ptr_at(storage_type* p, size_t i) { + return launder(reinterpret_cast<T*>(&p[i])); + } + + static const T* ptr_at(const storage_type* p, size_t i) { + return launder(reinterpret_cast<const T*>(&p[i])); + } + + static void move_storage(storage_type* src, storage_type* dest, size_t n) { + for (size_t i = 0; i < n; ++i) { + T* src_item = ptr_at(src, i); + T* dest_item = ptr_at(dest, i); + new (dest_item) T(std::move(*src_item)); + src_item->~T(); + } + } + + static void destroy_storage(storage_type* p, size_t n) { + for (size_t i = 0; i < n; ++i) { + ptr_at(p, i)->~T(); + } + } +}; + +template <typename T, size_t N, bool NonTrivialDestructor> +class StaticVectorBaseStorage : public StaticVectorMixin<T> { + protected: + using typename StaticVectorMixin<T>::storage_type; + + storage_type static_data_[N]; + size_t size_ = 0; + + void destroy() {} +}; + +template <typename T, size_t N> +class StaticVectorBaseStorage<T, N, true> : public StaticVectorMixin<T> { + protected: + using typename StaticVectorMixin<T>::storage_type; + + storage_type static_data_[N]; + size_t size_ = 0; + + ~StaticVectorBaseStorage() noexcept { destroy(); } + + void destroy() noexcept { this->destroy_storage(static_data_, size_); } +}; + +template <typename T, size_t N, bool D = !std::is_trivially_destructible<T>::value> +class StaticVectorBase : public StaticVectorBaseStorage<T, N, D> { + protected: + using Base = StaticVectorBaseStorage<T, N, D>; + using typename Base::storage_type; + + using Base::size_; + using Base::static_data_; + + StaticVectorBase() noexcept = default; + + storage_type* data_ptr() { return static_data_; } + + constexpr const storage_type* const_data_ptr() const { return static_data_; } + + void bump_size(size_t addend) { + assert(size_ + addend <= N); + size_ += addend; + } + + void reduce_size(size_t reduce_by) { + assert(reduce_by <= size_); + size_ -= reduce_by; + } + + void move_from(StaticVectorBase&& other) noexcept { + size_ = other.size_; + this->move_storage(other.static_data_, static_data_, size_); + other.size_ = 0; + } + + public: + constexpr size_t capacity() const { return N; } + + constexpr size_t max_size() const { return N; } + + void reserve(size_t n) {} + + void clear() { + this->destroy_storage(static_data_, size_); + size_ = 0; + } +}; + +template <typename T, size_t N> +class SmallVectorBase : public StaticVectorMixin<T> { + protected: + using typename StaticVectorMixin<T>::storage_type; + + storage_type static_data_[N]; + size_t size_ = 0; + storage_type* data_ = static_data_; + size_t dynamic_capacity_ = 0; Review comment: This uses 24 bytes in addition to the static elements. I think it'd be worthwhile to compress this further. Here's a sketch which uses a minimum of 16 bytes (for example, `SmallVector<int32_t, 3>` would be only 16 bytes) ```c++ template <typename T, size_t N> struct LittleEndianState { using Storage = StaticVectorMixin<T>; using storage_type = typename Storage::storage_type; struct DynamicState { // low bit will be zero for alignment T* data_; uint32_t size_, capacity_; }; struct SmallState { // low bit will be one for discrimination uint8_t shifted_size_; storage_type storage_[N]; size_t size() const { return shifted_size_ >> 1; } }; union { // low bit will be set if small uint8_t discriminant_; DynamicState dynamic_; SmallState small_; }; bool is_small() const { return discriminant_ & 1; } size_t size() const { return is_small() ? small_.size() >> 1 : dynamic_.size_; } }; template <typename T, size_t N> struct BigEndianState { using Storage = StaticVectorMixin<T>; using storage_type = typename Storage::storage_type; struct DynamicState { // high bit will be zero for discrimination uint32_t size_, capacity_; T* data_; }; struct SmallState { // high bit will be one for discrimination uint8_t shifted_size_; storage_type storage_[N]; size_t size() const { return shifted_size_ & 0b0111'1111; } }; union { // high bit will be set if small uint8_t discriminant_; DynamicState dynamic_; SmallState small_; }; bool is_small() const { return discriminant_ & 0b1000'0000; } size_t size() const { return is_small() ? small_.size() >> 1 : dynamic_.size_; } }; template <typename T, size_t N> struct SmallVector { #ifdef BIGENDIAN using State = BigEndianState<T, N>; #else using State = LittleEndianState<T, N>; #endif State state_; using Storage = StaticVectorMixin<T>; using storage_type = typename Storage::storage_type; T* data() { return state_.is_small() ? Storage::ptr_at(state_.small_.storage_, 0) : state_.dynamic_.data_; } ~SmallVector() { if (state_.is_small()) { Storage::destroy_storage(state_.small_.storage_, state_.small_.size()); } else { delete[] state_.dynamic_.data_; } } // ... }; ``` ########## File path: cpp/src/arrow/util/small_vector.h ########## @@ -0,0 +1,509 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +#pragma once + +#include <algorithm> +#include <cassert> +#include <cstddef> +#include <initializer_list> +#include <limits> +#include <new> +#include <type_traits> +#include <utility> + +#include "arrow/util/macros.h" + +namespace arrow { +namespace internal { + +#if __cplusplus >= 201703L +using std::launder; +#else +// TODO factor out from result.h + +// template <class T> +// constexpr T* launder(T* p) noexcept { +// return p; +// } +#endif + +template <typename ValueType, typename PointerType, typename ReferenceType> +class VectorIterator { Review comment: I'm not sure this is worthwhile; `std::iterator_traits` is already specialized for `int*` and `const int*` so I think you could just `using iterator = int*; using const_iterator = const int*;` below -- This is an automated message from the Apache Git Service. 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