From 9068e2071cd6983f04732947a5cef4926a84c531 Mon Sep 17 00:00:00 2001
From: Michael Scire <SciresM@gmail.com>
Date: Thu, 16 Jan 2020 04:09:11 -0800
Subject: [PATCH] offsetof: proper detection when sizeof() != alignof

---
 .../vapours/util/util_parent_of_member.hpp      | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/libraries/libvapours/include/vapours/util/util_parent_of_member.hpp b/libraries/libvapours/include/vapours/util/util_parent_of_member.hpp
index 8de42b9a4..14c7a3499 100644
--- a/libraries/libvapours/include/vapours/util/util_parent_of_member.hpp
+++ b/libraries/libvapours/include/vapours/util/util_parent_of_member.hpp
@@ -22,14 +22,15 @@ namespace ams::util {
 
     namespace impl {
 
-        template<size_t Alignment>
+        template<size_t MaxDepth>
         struct OffsetOfUnionHolder {
             template<typename ParentType, typename MemberType, size_t Offset>
             union UnionImpl {
+                using PaddingMember = std::array<char, alignof(ParentType)>;
                 static constexpr size_t GetOffset() { return Offset; }
 
                 struct {
-                    char padding[Offset];
+                    PaddingMember padding[Offset];
                     MemberType members[(sizeof(ParentType) / sizeof(MemberType)) + 1];
                 } data;
                 UnionImpl<ParentType, MemberType, Offset + 1> next_union;
@@ -46,12 +47,12 @@ namespace ams::util {
             };
 
             template<typename ParentType, typename MemberType>
-            union UnionImpl<ParentType, MemberType, Alignment> { /* Empty */ };
+            union UnionImpl<ParentType, MemberType, MaxDepth> { /* Empty */ };
         };
 
         template<typename ParentType, typename MemberType>
         struct OffsetOfCalculator {
-            using UnionHolder = typename OffsetOfUnionHolder<alignof(MemberType)>::template UnionImpl<ParentType, MemberType, 0>;
+            using UnionHolder = typename OffsetOfUnionHolder<sizeof(MemberType) / alignof(MemberType) + 1>::template UnionImpl<ParentType, MemberType, 0>;
             union Union {
                 char c;
                 UnionHolder first_union;
@@ -80,15 +81,15 @@ namespace ams::util {
                 const auto start  = std::addressof(cur_union.data.members[0]);
                 const auto next   = GetNextAddress(start, target);
 
-                if (next < target) {
-                    if constexpr (Offset + 1 < alignof(MemberType)) {
+                if (next != target) {
+                    if constexpr (Offset < sizeof(MemberType) / alignof(MemberType)) {
                         return OffsetOfImpl(member, cur_union.next_union);
                     } else {
-                        static_assert(Offset + 1 <= alignof(MemberType));
+                        std::abort();
                     }
                 }
 
-                return (next - start) * sizeof(MemberType) + Offset;
+                return (next - start) * sizeof(MemberType) + Offset * alignof(MemberType);
             }