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Cache also failed casts. #5

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Cache also failed casts. #5

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31 changes: 23 additions & 8 deletions fast_dynamic_cast.h
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Original file line number Diff line number Diff line change
Expand Up @@ -39,8 +39,10 @@
// conversion yet. Should be a fairly high value to avoid collisions.
#if _WIN64
#define DCAST_NO_OFFSET 0x7FFFFFFFFFFFFFFFLL
#define DCAST_FAILED 0x7FFFFFFFFFFFFFFELL
#else
#define DCAST_NO_OFFSET 0x7FFFFFFLL
#define DCAST_FAILED 0x7FFFFFELL
#endif

// Declare variables as thread local when using multithreaded dcast
Expand Down Expand Up @@ -95,18 +97,31 @@ namespace fast_dcast
v_table_ptr this_vtable = get_vtable(ptr);
if (offset != DCAST_NO_OFFSET && src_vtable_ptr == this_vtable)
{
// In case we have a cache hit, casting the pointer is straightforward
char* new_ptr = reinterpret_cast<char*>(ptr) + offset;
return reinterpret_cast<_To>(new_ptr);
// Cache hit, first check the failed cast marker
if (offset == DCAST_FAILED)
{
return nullptr;
}
else
{
// In case we have a cache hit, casting the pointer is straightforward
char* new_ptr = reinterpret_cast<char*>(ptr) + offset;
return reinterpret_cast<_To>(new_ptr);
}
}
else {
else
{
// Need to construct cache entry
auto result = dynamic_cast<_To>(ptr);
if (result == nullptr)
return nullptr;

src_vtable_ptr = this_vtable;
offset = reinterpret_cast<const char*>(result) - reinterpret_cast<const char*>(ptr);
if (result == nullptr)
{
offset = DCAST_FAILED;
}
else
{
offset = reinterpret_cast<const char*>(result) - reinterpret_cast<const char*>(ptr);
}
return result;
}
};
Expand Down