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https://github.com/Atmosphere-NX/Atmosphere.git
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util: improve (and use) offsetof that's """standard compliant"""
This commit is contained in:
Michael Scire
parent
ad4c794aea
commit
ec6d1a92ef
2 changed files with 71 additions and 87 deletions
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@ -502,7 +502,7 @@ namespace ams::util {
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return util::GetParentPointer<Member, Derived>(node);
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}
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private:
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static_assert(util::IsAligned(util::impl::OffsetOf<Member, Derived>::Value, alignof(void *)));
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static_assert(util::IsAligned(util::impl::OffsetOf<Member, Derived>::value, alignof(void *)));
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};
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template<auto T, class Derived = util::impl::GetParentType<T>>
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@ -516,7 +516,7 @@ namespace ams::util {
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using TreeTypeImpl = impl::IntrusiveRedBlackTreeImpl;
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static constexpr bool IsValid() {
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return util::IsAligned(util::impl::OffsetOf<Member, Derived>::Value, alignof(void *));
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return util::IsAligned(util::impl::OffsetOf<Member, Derived>::value, alignof(void *));
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}
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private:
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template<class, class, class>
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@ -23,98 +23,85 @@ namespace ams::util {
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namespace impl {
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#define AMS_UTIL_OFFSET_OF_STANDARD_COMPLIANT 0
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#define AMS_UTIL_OFFSET_OF_STANDARD_COMPLIANT 1
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#if AMS_UTIL_OFFSET_OF_STANDARD_COMPLIANT
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template<size_t MaxDepth>
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struct OffsetOfUnionHolder {
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template<typename ParentType, typename MemberType, size_t Offset>
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union UnionImpl {
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using PaddingMember = char;
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static constexpr size_t GetOffset() { return Offset; }
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template<std::ptrdiff_t Offset, typename P, typename M, auto Ptr>
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consteval std::strong_ordering TestOffsetForOffsetOfImpl() {
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#pragma pack(push, 1)
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struct {
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PaddingMember padding[Offset];
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MemberType members[(sizeof(ParentType) / sizeof(MemberType)) + 1];
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} data;
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#pragma pack(pop)
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UnionImpl<ParentType, MemberType, Offset + 1> next_union;
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};
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template<typename ParentType, typename MemberType>
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union UnionImpl<ParentType, MemberType, MaxDepth> { /* Empty ... */ };
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};
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template<typename ParentType, typename MemberType>
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struct OffsetOfCalculator {
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using UnionHolder = typename OffsetOfUnionHolder<sizeof(MemberType)>::template UnionImpl<ParentType, MemberType, 0>;
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union Union {
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const union Union {
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char c;
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UnionHolder first_union;
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ParentType parent;
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/* This coerces the active member to be c. */
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constexpr Union() : c() { /* ... */ }
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constexpr ~Union() { std::destroy_at(std::addressof(c)); }
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struct {
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char padding[Offset];
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M members[1 + (sizeof(P) / std::max<size_t>(sizeof(M), 1))];
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};
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static constexpr Union U = {};
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P p;
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static constexpr const MemberType *GetNextAddress(const MemberType *start, const MemberType *target) {
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while (start < target) {
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start++;
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}
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return start;
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constexpr Union() : c() { /* ... */ }
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constexpr ~Union() { /* ... */ }
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} U;
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#pragma pack(pop)
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const M *target = std::addressof(U.p.*Ptr);
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const M *guess = std::addressof(U.members[0]);
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/* NOTE: target == guess is definitely legal, target < guess is probably legal, definitely legal if Offset <= true offsetof. */
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/* <=> may or may not be legal, but it definitely seems to work. Evaluate again, if it breaks. */
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return guess <=> target;
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//if (guess == target) {
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// return std::strong_ordering::equal;
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//} else if (guess < target) {
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// return std::strong_ordering::less;
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//} else {
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// return std::strong_ordering::greater;
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//}
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}
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static constexpr std::ptrdiff_t GetDifference(const MemberType *start, const MemberType *target) {
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return (target - start) * sizeof(MemberType);
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}
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template<std::ptrdiff_t Low, std::ptrdiff_t High, typename P, typename M, auto Ptr>
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consteval std::ptrdiff_t OffsetOfImpl() {
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static_assert(Low <= High);
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template<typename CurUnion>
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static constexpr std::ptrdiff_t OffsetOfImpl(MemberType ParentType::*member, CurUnion &cur_union) {
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constexpr size_t Offset = CurUnion::GetOffset();
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const auto target = std::addressof(U.parent.*member);
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const auto start = std::addressof(cur_union.data.members[0]);
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const auto next = GetNextAddress(start, target);
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constexpr std::ptrdiff_t Guess = (Low + High) / 2;
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constexpr auto Order = TestOffsetForOffsetOfImpl<Guess, P, M, Ptr>();
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if (next != target) {
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if constexpr (Offset < sizeof(MemberType) - 1) {
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return OffsetOfImpl(member, cur_union.next_union);
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if constexpr (Order == std::strong_ordering::equal) {
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return Guess;
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} else if constexpr (Order == std::strong_ordering::less) {
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return OffsetOfImpl<Guess + 1, High, P, M, Ptr>();
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} else {
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__builtin_unreachable();
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static_assert(Order == std::strong_ordering::greater);
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return OffsetOfImpl<Low, Guess - 1, P, M, Ptr>();
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}
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}
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return (next - start) * sizeof(MemberType) + Offset;
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}
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static constexpr std::ptrdiff_t OffsetOf(MemberType ParentType::*member) {
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return OffsetOfImpl(member, U.first_union);
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}
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template<typename P, typename M, auto Ptr>
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struct OffsetOfCalculator {
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static constexpr const std::ptrdiff_t Value = OffsetOfImpl<0, sizeof(P), P, M, Ptr>();
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};
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#else
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template<typename T>
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union HelperUnion {
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T v;
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template<typename ParentType, typename MemberType, auto Ptr>
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struct OffsetOfCalculator {
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private:
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static consteval std::ptrdiff_t Calculate() {
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const union Union {
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ParentType p;
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char c;
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constexpr HelperUnion() : c() { /* ... */ }
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constexpr ~HelperUnion() { std::destroy_at(std::addressof(c)); }
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};
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constexpr Union() : c() { /* ... */ }
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constexpr ~Union() { /* ... */ }
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} U;
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const auto *parent = std::addressof(U.p);
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const auto *target = std::addressof(parent->*Ptr);
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template<typename ParentType, typename MemberType>
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struct OffsetOfCalculator {
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static constexpr std::ptrdiff_t OffsetOf(MemberType ParentType::*member) {
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constexpr HelperUnion<ParentType> Holder = {};
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const auto *parent = std::addressof(Holder.v);
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const auto *target = std::addressof(parent->*member);
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return static_cast<const uint8_t *>(static_cast<const void *>(target)) - static_cast<const uint8_t *>(static_cast<const void *>(parent));
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}
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public:
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static constexpr const std::ptrdiff_t Value = Calculate();
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};
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#endif
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@ -135,22 +122,19 @@ namespace ams::util {
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using GetMemberType = typename GetMemberPointerTraits<decltype(MemberPtr)>::Member;
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template<auto MemberPtr, typename RealParentType = GetParentType<MemberPtr>> requires (std::derived_from<RealParentType, GetParentType<MemberPtr>> || std::same_as<RealParentType, GetParentType<MemberPtr>>)
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struct OffsetOf {
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using MemberType = GetMemberType<MemberPtr>;
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struct OffsetOf : public std::integral_constant<std::ptrdiff_t, OffsetOfCalculator<RealParentType, GetMemberType<MemberPtr>, MemberPtr>::Value> {};
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static constexpr std::ptrdiff_t Value = OffsetOfCalculator<RealParentType, MemberType>::OffsetOf(MemberPtr);
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};
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}
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template<auto MemberPtr, typename RealParentType = impl::GetParentType<MemberPtr>>
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ALWAYS_INLINE RealParentType &GetParentReference(impl::GetMemberType<MemberPtr> *member) {
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constexpr std::ptrdiff_t Offset = impl::OffsetOf<MemberPtr, RealParentType>::Value;
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constexpr std::ptrdiff_t Offset = impl::OffsetOf<MemberPtr, RealParentType>::value;
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return *static_cast<RealParentType *>(static_cast<void *>(static_cast<uint8_t *>(static_cast<void *>(member)) - Offset));
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}
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template<auto MemberPtr, typename RealParentType = impl::GetParentType<MemberPtr>>
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ALWAYS_INLINE RealParentType const &GetParentReference(impl::GetMemberType<MemberPtr> const *member) {
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constexpr std::ptrdiff_t Offset = impl::OffsetOf<MemberPtr, RealParentType>::Value;
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constexpr std::ptrdiff_t Offset = impl::OffsetOf<MemberPtr, RealParentType>::value;
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return *static_cast<const RealParentType *>(static_cast<const void *>(static_cast<const uint8_t *>(static_cast<const void *>(member)) - Offset));
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}
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@ -187,7 +171,7 @@ namespace ams::util {
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/* Defines, for use by other code. */
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#define OFFSETOF(parent, member) (::ams::util::impl::OffsetOf<&parent::member, parent>::Value)
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#define OFFSETOF(parent, member) (::ams::util::impl::OffsetOf<&parent::member, parent>::value)
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#define GET_PARENT_PTR(parent, member, _arg) (::ams::util::GetParentPointer<&parent::member, parent>(_arg))
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