Remove bitfield.h
Summary: ##Changelog: [Internal][Yoga] Remove Bitfield.h Reviewed By: astreet Differential Revision: D18519647 fbshipit-source-id: b46fe585d3ef5f1da7d2726b2d9f759a649be121
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/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*/
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#pragma once
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#include <cstddef>
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#include <limits>
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#include <type_traits>
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#include <yoga/YGEnums.h>
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namespace facebook {
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namespace yoga {
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namespace detail {
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constexpr size_t log2ceil(size_t n) {
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return n < 1 ? 0 : (1 + log2ceil(n / 2));
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}
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// The number of bits necessary to represent enums defined with YG_ENUM_SEQ_DECL
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template <typename Enum>
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constexpr size_t bitWidth() {
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static_assert(
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enums::count<Enum>() > 0, "Enums must have at least one entries");
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return log2ceil(enums::count<Enum>() - 1);
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}
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// Number of bits needed for a boolean
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template <>
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constexpr size_t bitWidth<bool>() {
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return 1;
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}
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template <typename U, typename... Ts>
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struct BitTraits {};
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template <typename U>
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struct BitTraits<U> {
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// Base cases
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static constexpr size_t width(size_t) { return 0; }
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static constexpr size_t shift(size_t) { return 0; }
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};
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template <typename U, typename T, typename... Ts>
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struct BitTraits<U, T, Ts...> {
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using Rest = BitTraits<U, Ts...>;
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static constexpr size_t width(size_t idx) {
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return idx == 0 ? bitWidth<T>() : Rest::width(idx - 1);
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}
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static constexpr size_t shift(size_t idx) {
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return idx == 0 ? Rest::width(0) + Rest::shift(0) : Rest::shift(idx - 1);
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}
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static constexpr U mask(size_t idx) {
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return ((U{1} << width(idx)) - 1) << shift(idx);
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}
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};
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template <size_t Idx, typename T, typename... Ts>
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struct IndexedType {
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using Type = typename IndexedType<Idx - 1, Ts...>::Type;
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};
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template <typename T, typename... Ts>
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struct IndexedType<0, T, Ts...> {
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using Type = T;
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};
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} // namespace detail
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template <typename Storage, typename... Fields>
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class Bitfield {
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static_assert(
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std::is_integral<Storage>::value,
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"Bitfield needs an integral storage type");
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static_assert(
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std::is_unsigned<Storage>::value,
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"Bitfield needs an unsigned storage type");
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static_assert(sizeof...(Fields) > 0, "Bitfield needs at least one member");
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using BitTraits = detail::BitTraits<Storage, Fields...>;
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#if !defined(_MSC_VER) || _MSC_VER > 1914
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static_assert(
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BitTraits::shift(0) + BitTraits::width(0) <=
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std::numeric_limits<Storage>::digits,
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"Specified storage type is too narrow to hold all types");
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#endif
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template <size_t Idx>
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using TypeAt = typename detail::IndexedType<Idx, Fields...>::Type;
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template <size_t Idx, typename Value, typename... Values>
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static constexpr Storage initStorage(Value value, Values... values) {
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return ((value << BitTraits::shift(Idx)) & BitTraits::mask(Idx)) |
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initStorage<Idx + 1, Values...>(values...);
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}
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template <size_t Idx>
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static constexpr Storage initStorage() {
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return Storage{0};
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}
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Storage storage_ = 0;
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public:
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template <size_t Idx>
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class Ref {
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Bitfield& bitfield_;
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public:
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Ref(Bitfield& bitfield) : bitfield_(bitfield) {}
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Ref& operator=(TypeAt<Idx> value) {
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bitfield_.storage_ = (bitfield_.storage_ & ~BitTraits::mask(Idx)) |
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((value << BitTraits::shift(Idx)) & BitTraits::mask(Idx));
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return *this;
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}
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operator TypeAt<Idx>() const {
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return const_cast<const Bitfield&>(bitfield_).at<Idx>();
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}
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};
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constexpr Bitfield() = default;
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constexpr Bitfield(Fields... values) : storage_{initStorage<0>(values...)} {}
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template <size_t Idx>
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constexpr TypeAt<Idx> at() const {
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return static_cast<TypeAt<Idx>>(
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(storage_ & BitTraits::mask(Idx)) >> BitTraits::shift(Idx));
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}
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template <size_t Idx>
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Ref<Idx> at() {
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return {*this};
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}
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};
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} // namespace yoga
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} // namespace facebook
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