Source/JavaScriptCore/runtime/StringSplitCache.h

/*
 * Copyright (C) 2023 Apple Inc. All rights reserved.
 * Copyright (C) 2012 the V8 project authors. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    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,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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#pragma once

#include <JavaScriptCore/MatchResult.h>
#include <array>
#include <wtf/DebugHeap.h>
#include <wtf/HashFunctions.h>
#include <wtf/Noncopyable.h>
#include <wtf/RefPtr.h>
#include <wtf/TZoneMalloc.h>
#include <wtf/text/AtomStringImpl.h>

namespace JSC {

DECLARE_ALLOCATOR_WITH_HEAP_IDENTIFIER_AND_EXPORT(StringSplitCache, WTF_INTERNAL);

class JSCellButterfly;
class RegExp;

class StringSplitCache {
    WTF_MAKE_TZONE_ALLOCATED(StringSplitCache);
    WTF_MAKE_NONCOPYABLE(StringSplitCache);
public:
    StringSplitCache() = default;

    struct StringEntry {
        RefPtr<AtomStringImpl> m_subject { nullptr };
        RefPtr<AtomStringImpl> m_separator { nullptr };
        JSCellButterfly* m_butterfly { nullptr };
    };

    struct RegExpEntry {
        RefPtr<AtomStringImpl> m_subject { nullptr };
        RegExp* m_regExp { nullptr };
        JSCellButterfly* m_butterfly { nullptr };
        MatchResult m_lastMatch { };
    };

    JSCellButterfly* getForString(const String& subject, const String& separator);
    void setForString(const String& subject, const String& separator, JSCellButterfly*);

    JSCellButterfly* getForRegExp(const String& subject, RegExp*, MatchResult& lastMatch);
    void setForRegExp(const String& subject, RegExp*, JSCellButterfly*, MatchResult lastMatch);

    void clear()
    {
        m_stringEntries.fill(StringEntry { });
        m_regExpEntries.fill(RegExpEntry { });
    }

private:
    static constexpr unsigned stringCacheSize = 64;
    static constexpr unsigned regExpCacheSize = 256;
    static_assert(!(stringCacheSize & (stringCacheSize - 1)));
    static_assert(!(regExpCacheSize & (regExpCacheSize - 1)));

    size_t regExpEntryIndex(AtomStringImpl* subject, RegExp* regExp) const
    {
        return pairIntHash(subject->hash(), PtrHash<RegExp*>::hash(regExp)) & (m_regExpEntries.size() - 1);
    }

    std::array<StringEntry, stringCacheSize> m_stringEntries { };
    std::array<RegExpEntry, regExpCacheSize> m_regExpEntries { };
};

} // namespace JSC