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util: faster constexpr offsetof calc, at the cost of standards compliance

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Michael Scire 2021-01-08 04:07:42 -08:00
parent a6e3a93c07
commit b8072b1398
1 changed files with 84 additions and 66 deletions
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150
libraries/libvapours/include/vapours/util/util_parent_of_member.hpp
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@ -23,83 +23,101 @@ namespace ams::util {
namespace impl {
template<size_t MaxDepth>
struct OffsetOfUnionHolder {
template<typename ParentType, typename MemberType, size_t Offset>
union UnionImpl {
using PaddingMember = char;
static constexpr size_t GetOffset() { return Offset; }
#define AMS_UTIL_OFFSET_OF_STANDARD_COMPLIANT 0
#pragma pack(push, 1)
struct {
PaddingMember padding[Offset];
MemberType members[(sizeof(ParentType) / sizeof(MemberType)) + 1];
} data;
#pragma pack(pop)
UnionImpl<ParentType, MemberType, Offset + 1> next_union;
#if AMS_UTIL_OFFSET_OF_STANDARD_COMPLIANT
template<size_t MaxDepth>
struct OffsetOfUnionHolder {
template<typename ParentType, typename MemberType, size_t Offset>
union UnionImpl {
using PaddingMember = char;
static constexpr size_t GetOffset() { return Offset; }
#pragma pack(push, 1)
struct {
PaddingMember padding[Offset];
MemberType members[(sizeof(ParentType) / sizeof(MemberType)) + 1];
} data;
#pragma pack(pop)
UnionImpl<ParentType, MemberType, Offset + 1> next_union;
};
template<typename ParentType, typename MemberType>
union UnionImpl<ParentType, MemberType, 0> {
static constexpr size_t GetOffset() { return 0; }
struct {
MemberType members[(sizeof(ParentType) / sizeof(MemberType)) + 1];
} data;
UnionImpl<ParentType, MemberType, 1> next_union;
};
template<typename ParentType, typename MemberType>
union UnionImpl<ParentType, MemberType, MaxDepth> { /* Empty ... */ };
};
template<typename ParentType, typename MemberType>
union UnionImpl<ParentType, MemberType, 0> {
static constexpr size_t GetOffset() { return 0; }
struct OffsetOfCalculator {
using UnionHolder = typename OffsetOfUnionHolder<sizeof(MemberType)>::template UnionImpl<ParentType, MemberType, 0>;
union Union {
char c;
UnionHolder first_union;
TYPED_STORAGE(ParentType) parent;
struct {
MemberType members[(sizeof(ParentType) / sizeof(MemberType)) + 1];
} data;
UnionImpl<ParentType, MemberType, 1> next_union;
};
/* This coerces the active member to be c. */
constexpr Union() : c() { /* ... */ }
};
static constexpr Union U = {};
template<typename ParentType, typename MemberType>
union UnionImpl<ParentType, MemberType, MaxDepth> { /* Empty ... */ };
};
template<typename ParentType, typename MemberType>
struct OffsetOfCalculator {
using UnionHolder = typename OffsetOfUnionHolder<sizeof(MemberType)>::template UnionImpl<ParentType, MemberType, 0>;
union Union {
char c;
UnionHolder first_union;
TYPED_STORAGE(ParentType) parent;
/* This coerces the active member to be c. */
constexpr Union() : c() { /* ... */ }
};
static constexpr Union U = {};
static constexpr const MemberType *GetNextAddress(const MemberType *start, const MemberType *target) {
while (start < target) {
start++;
}
return start;
}
static constexpr std::ptrdiff_t GetDifference(const MemberType *start, const MemberType *target) {
return (target - start) * sizeof(MemberType);
}
template<typename CurUnion>
static constexpr std::ptrdiff_t OffsetOfImpl(MemberType ParentType::*member, CurUnion &cur_union) {
constexpr size_t Offset = CurUnion::GetOffset();
const auto target = std::addressof(GetPointer(U.parent)->*member);
const auto start = std::addressof(cur_union.data.members[0]);
const auto next = GetNextAddress(start, target);
if (next != target) {
if constexpr (Offset < sizeof(MemberType) - 1) {
return OffsetOfImpl(member, cur_union.next_union);
} else {
__builtin_unreachable();
static constexpr const MemberType *GetNextAddress(const MemberType *start, const MemberType *target) {
while (start < target) {
start++;
}
return start;
}
return (next - start) * sizeof(MemberType) + Offset;
}
static constexpr std::ptrdiff_t GetDifference(const MemberType *start, const MemberType *target) {
return (target - start) * sizeof(MemberType);
}
template<typename CurUnion>
static constexpr std::ptrdiff_t OffsetOfImpl(MemberType ParentType::*member, CurUnion &cur_union) {
constexpr size_t Offset = CurUnion::GetOffset();
const auto target = std::addressof(GetPointer(U.parent)->*member);
const auto start = std::addressof(cur_union.data.members[0]);
const auto next = GetNextAddress(start, target);
if (next != target) {
if constexpr (Offset < sizeof(MemberType) - 1) {
return OffsetOfImpl(member, cur_union.next_union);
} else {
__builtin_unreachable();
}
}
return (next - start) * sizeof(MemberType) + Offset;
}
static constexpr std::ptrdiff_t OffsetOf(MemberType ParentType::*member) {
return OffsetOfImpl(member, U.first_union);
}
};
static constexpr std::ptrdiff_t OffsetOf(MemberType ParentType::*member) {
return OffsetOfImpl(member, U.first_union);
}
};
#else
template<typename ParentType, typename MemberType>
struct OffsetOfCalculator {
static constexpr std::ptrdiff_t OffsetOf(MemberType ParentType::*member) {
constexpr TYPED_STORAGE(ParentType) Holder = {};
const auto *parent = GetPointer(Holder);
const auto *target = std::addressof(parent->*member);
return static_cast<const uint8_t *>(static_cast<const void *>(target)) - static_cast<const uint8_t *>(static_cast<const void *>(parent));
}
};
#endif
template<typename T>
struct GetMemberPointerTraits;