serenity/AK/StringImpl.h

/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 * 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 THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 THE COPYRIGHT HOLDER 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 PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#pragma once

#include <AK/Badge.h>
#include <AK/RefCounted.h>
#include <AK/RefPtr.h>
#include <AK/Span.h>
#include <AK/Types.h>
#include <AK/kmalloc.h>

namespace AK {

enum ShouldChomp {
    NoChomp,
    Chomp
};

class StringImpl : public RefCounted<StringImpl> {
public:
    static NonnullRefPtr<StringImpl> create_uninitialized(size_t length, char*& buffer);
    static RefPtr<StringImpl> create(const char* cstring, ShouldChomp = NoChomp);
    static RefPtr<StringImpl> create(const char* cstring, size_t length, ShouldChomp = NoChomp);
    static RefPtr<StringImpl> create(ReadonlyBytes, ShouldChomp = NoChomp);
    NonnullRefPtr<StringImpl> to_lowercase() const;
    NonnullRefPtr<StringImpl> to_uppercase() const;

    void operator delete(void* ptr)
    {
        kfree(ptr);
    }

    static StringImpl& the_empty_stringimpl();

    ~StringImpl();

    size_t length() const { return m_length; }
    // Includes NUL-terminator.
    const char* characters() const { return &m_inline_buffer[0]; }

    ALWAYS_INLINE ReadonlyBytes bytes() const { return { characters(), length() }; }

    const char& operator[](size_t i) const
    {
        ASSERT(i < m_length);
        return characters()[i];
    }

    bool operator==(const StringImpl& other) const
    {
        if (length() != other.length())
            return false;
        return !__builtin_memcmp(characters(), other.characters(), length());
    }

    unsigned hash() const
    {
        if (!m_has_hash)
            compute_hash();
        return m_hash;
    }

    unsigned existing_hash() const
    {
        return m_hash;
    }

    bool is_fly() const { return m_fly; }
    void set_fly(Badge<FlyString>, bool fly) const { m_fly = fly; }

private:
    enum ConstructTheEmptyStringImplTag {
        ConstructTheEmptyStringImpl
    };
    explicit StringImpl(ConstructTheEmptyStringImplTag)
        : m_fly(true)
    {
        m_inline_buffer[0] = '\0';
    }

    enum ConstructWithInlineBufferTag {
        ConstructWithInlineBuffer
    };
    StringImpl(ConstructWithInlineBufferTag, size_t length);

    void compute_hash() const;

    size_t m_length { 0 };
    mutable unsigned m_hash { 0 };
    mutable bool m_has_hash { false };
    mutable bool m_fly { false };
    char m_inline_buffer[0];
};

inline constexpr u32 string_hash(const char* characters, size_t length)
{
    u32 hash = 0;
    for (size_t i = 0; i < length; ++i) {
        hash += (u32)characters[i];
        hash += (hash << 10);
        hash ^= (hash >> 6);
    }
    hash += hash << 3;
    hash ^= hash >> 11;
    hash += hash << 15;
    return hash;
}

}

using AK::Chomp;
using AK::string_hash;
using AK::StringImpl;