Source/JavaScriptCore/wasm/WasmIndexOrName.h

/*
 * Copyright (C) 2017 Apple Inc. All rights reserved.
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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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 * 2. Redistributions in binary form must reproduce the above copyright
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 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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#pragma once

#include "WasmName.h"
#include "WasmNameSection.h"
#include <wtf/RefPtr.h>
#include <wtf/StdLibExtras.h>
#include <wtf/text/WTFString.h>

namespace JSC { namespace Wasm {

struct NameSection;

// Keep this class copyable when the world is stopped: do not allocate any memory while copying this.
// SamplingProfiler copies it while suspending threads.
struct IndexOrName {
    typedef size_t Index;

    IndexOrName() { m_indexName.index = emptyTag; }
    IndexOrName(Index, std::pair<const Name*, RefPtr<NameSection>>&&);
    bool isEmpty() const { return bitwise_cast<Index>(m_indexName) & emptyTag; }
    bool isIndex() const { return bitwise_cast<Index>(m_indexName) & indexTag; }
    bool isName() const { return !(isEmpty() || isName()); }
    NameSection* nameSection() const { return m_nameSection.get(); }

    friend String makeString(const IndexOrName&);

private:
    union {
        Index index;
        const Name* name;
    } m_indexName;
    RefPtr<NameSection> m_nameSection;

    // Use the top bits as tags. Neither pointers nor the function index space should use them.
    static constexpr Index indexTag = 1ull << (CHAR_BIT * sizeof(Index) - 1);
    static constexpr Index emptyTag = 1ull << (CHAR_BIT * sizeof(Index) - 2);
    static constexpr Index allTags = indexTag | emptyTag;
};

String makeString(const IndexOrName&);

} } // namespace JSC::Wasm