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// slang-relative-ptr.h
#ifndef SLANG_RELATIVE_PTR_H
#define SLANG_RELATIVE_PTR_H
// This file implements a smart pointer type `RelativePtr<T>`
// that, rather than storing the actual *address* of a value
// of type `T`, stores the relative offset (in bytes) between
// the target `T*` and the address of the `RelativePtr<T>`
// itself.
//
// This kind of pointer representation can be useful when
// implementing "memory-mappable" data structures that can
// still conveniently represent complicated object graphs.
#include "slang-basic.h"
namespace Slang
{
namespace detail
{
struct RelativePtr32Traits
{
using Offset = Int32;
using UOffset = UInt32;
};
struct RelativePtr64Traits
{
using Offset = Int64;
using UOffset = UInt64;
};
} // namespace detail
template<typename T, typename Traits>
struct RelativePtr
{
public:
using This = RelativePtr<T, Traits>;
using Value = T;
using RawPtr = T*;
using Offset = typename Traits::Offset;
using UOffset = typename Traits::UOffset;
SLANG_FORCE_INLINE RelativePtr() = default;
SLANG_FORCE_INLINE RelativePtr(RelativePtr const& ptr) { set(ptr); }
SLANG_FORCE_INLINE RelativePtr(RelativePtr&& ptr) { set(ptr); }
SLANG_FORCE_INLINE RelativePtr(T* ptr) { set(ptr); }
SLANG_FORCE_INLINE void operator=(RelativePtr const& ptr) { set(ptr); }
SLANG_FORCE_INLINE void operator=(RelativePtr&& ptr) { set(ptr); }
SLANG_FORCE_INLINE void operator=(T* ptr) { set(ptr); }
T* get() const
{
if (_offset == 0)
{
return nullptr;
}
intptr_t thisAddr = intptr_t(this);
intptr_t targetAddr = thisAddr + intptr_t(_offset);
return (T*)(targetAddr);
}
void set(T* ptr)
{
if (ptr == nullptr)
{
_offset = 0;
return;
}
intptr_t thisAddr = intptr_t(this);
intptr_t targetAddr = intptr_t(ptr);
intptr_t offsetVal = targetAddr - thisAddr;
_offset = Offset(offsetVal);
SLANG_ASSERT(intptr_t(_offset) == offsetVal);
}
SLANG_FORCE_INLINE operator T*() const { return get(); }
SLANG_FORCE_INLINE T* operator->() const { return get(); }
private:
Offset _offset = 0;
};
template<typename T>
using RelativePtr32 = RelativePtr<T, detail::RelativePtr32Traits>;
template<typename T>
using RelativePtr64 = RelativePtr<T, detail::RelativePtr64Traits>;
} // namespace Slang
#endif
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