Source/WTF/wtf/CompactPtr.cpp

/*
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 * 1. Redistributions of source code must retain the above copyright
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#include "config.h"
#include <wtf/CompactPtr.h>

namespace WTF {

#if HAVE(36BIT_ADDRESS)

struct OutsizedCompactPtrManager {
    HashMap<void*, OutsizedCompactPtr::Encoded> addedPointers;
    SegmentedVector<void*> outsizedPointers;
};

static Lock outsizedCompactPtrLock;
static OutsizedCompactPtrManager* outsizedCompactPtrManager;

static void ensureOutsizedCompactPtrManager()
{
    static std::once_flag onceFlag;
    std::call_once(onceFlag, [] {
        // WTF::initialize() is only needed to ensure that lowestAccessibleAddress()
        // is ready for use.
        WTF::initialize();
        RELEASE_ASSERT(lowestAccessibleAddress() >= OutsizedCompactPtr::addressRangeForOutsizedPtrEncoding);

        static NeverDestroyed<OutsizedCompactPtrManager> manager;
        outsizedCompactPtrManager = &manager.get();
    });
}

OutsizedCompactPtr::Encoded OutsizedCompactPtr::encode(void* ptr)
{
    if (!outsizedCompactPtrManager)
        ensureOutsizedCompactPtrManager();

    Locker locker { outsizedCompactPtrLock };

    auto& addedPointers = outsizedCompactPtrManager->addedPointers;
    auto iter = addedPointers.find(ptr);
    if (iter != addedPointers.end())
        return iter->value;

    auto& outsizedPointers = outsizedCompactPtrManager->outsizedPointers;
    size_t entryIndex = outsizedPointers.size();
    Encoded encoded = entryIndex + OutsizedCompactPtr::minEncoding;
    RELEASE_ASSERT(encoded < OutsizedCompactPtr::maxEncoding, encoded, OutsizedCompactPtr::maxEncoding);
    addedPointers.add(ptr, encoded);
    outsizedPointers.append(ptr);

    return encoded;
}

void* OutsizedCompactPtr::decode(uint32_t encoded)
{
    Locker locker { outsizedCompactPtrLock };
    auto& outsizedPointers = outsizedCompactPtrManager->outsizedPointers;
    size_t entryIndex = encoded - OutsizedCompactPtr::minEncoding;
    RELEASE_ASSERT(entryIndex < outsizedPointers.size(), entryIndex, outsizedPointers.size());
    return outsizedPointers[entryIndex];
}

#endif // HAVE(36BIT_ADDRESS)

} // namespace WTF