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NFC: Add FreeObject::from_next_ptr

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Rather than open-code the conversion from &f->next_object to f, add a static
method to FreeObject and take the opportunity to add a static_assert that our
reinterpret_cast is sound.
This commit is contained in:
Nathaniel Wesley Filardo
2021-09-21 12:23:10 +01:00
committed by Nathaniel Wesley Filardo
parent 06e333a3a9
commit 55cd5e87c0
1 changed files with 12 additions and 1 deletions
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13
src/mem/freelist.h
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@@ -184,6 +184,17 @@ namespace snmalloc
return p.template as_static<FreeObject::T<BQueue>>();
}
/**
* A container-of operation to convert &f->next_object to f
*/
template<SNMALLOC_CONCEPT(capptr::ConceptBound) BQueue>
static FreeObject::T<BQueue>*
from_next_ptr(CapPtr<FreeObject::T<BQueue>, BQueue>* ptr)
{
static_assert(offsetof(FreeObject::T<BQueue>, next_object) == 0);
return reinterpret_cast<FreeObject::T<BQueue>*>(ptr);
}
private:
/**
* Involutive encryption with raw pointers
@@ -655,7 +666,7 @@ namespace snmalloc
// to the actual object. This isn't true if the builder is
// empty, but you are not allowed to call this in the empty case.
auto last = FreeObject::HeadPtr<BView, BQueue>(
reinterpret_cast<FreeObject::T<BQueue>*>(end[0]));
FreeObject::from_next_ptr(cast_end(0)));
init();
return {first, last};
}