qoffsetstringarray_p.h

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// Copyright (C) 2020 The Qt Company Ltd.
// Copyright (C) 2021 Intel Corporation.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
#ifndef QOFFSETSTRINGARRAY_P_H
#define QOFFSETSTRINGARRAY_P_H
 
//
//  W A R N I N G
//  -------------
//
// This file is not part of the Qt API.  It exists purely as an
// implementation detail.  This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//
 
#include "private/qglobal_p.h"
 
#include <QByteArrayView>
 
#include <QtCore/q20algorithm.h>
#include <array>
#include <limits>
#include <string_view>
#include <tuple>
 
class tst_QOffsetStringArray;
 
QT_BEGIN_NAMESPACE
 
QT_WARNING_PUSH
#if defined(Q_CC_GNU_ONLY) && Q_CC_GNU >= 1100
// we usually don't overread, but GCC has a false positive
QT_WARNING_DISABLE_GCC("-Wstringop-overread")
#endif
 
 
template <typename StaticString, typename OffsetList>
class QOffsetStringArray
{
public:
    constexpr QOffsetStringArray(const StaticString &string, const OffsetList &offsets)
        : m_string(string), m_offsets(offsets)
    {}
 
    constexpr const char *operator[](const int index) const noexcept
    {
        return m_string.data() + m_offsets[qBound(int(0), index, count())];
    }
 
    constexpr const char *at(const int index) const noexcept
    {
        return m_string.data() + m_offsets[index];
    }
 
    constexpr QByteArrayView viewAt(qsizetype index) const noexcept
    {
        return { m_string.data() + m_offsets[index],
                    qsizetype(m_offsets[index + 1]) - qsizetype(m_offsets[index]) - 1 };
    }
 
    constexpr int count() const { return int(m_offsets.size()) - 1; }
 
    bool contains(QByteArrayView needle, Qt::CaseSensitivity cs = Qt::CaseSensitive) const noexcept
    {
        for (qsizetype i = 0; i < count(); ++i) {
            if (viewAt(i).compare(needle, cs) == 0)
                return true;
        }
        return false;
    }
 
private:
    StaticString m_string;
    OffsetList m_offsets;
    friend tst_QOffsetStringArray;
};
 
namespace QtPrivate {
template <size_t Highest> constexpr auto minifyValue()
{
    constexpr size_t max8 = (std::numeric_limits<quint8>::max)();
    constexpr size_t max16 = (std::numeric_limits<quint16>::max)();
    if constexpr (Highest <= max8) {
        return quint8(Highest);
    } else if constexpr (Highest <= max16) {
        return quint16(Highest);
    } else {
        // int is probably enough for everyone
        return int(Highest);
    }
}
 
template <size_t StringLength, typename Extractor, typename... T>
constexpr auto makeStaticString(Extractor extract, const T &... entries)
{
    std::array<char, StringLength> result = {};
    qptrdiff offset = 0;
 
    const char *strings[] = { extract(entries).operator const char *()... };
    size_t lengths[] = { sizeof(extract(T{}))... };
    for (size_t i = 0; i < std::size(strings); ++i) {
        q20::copy_n(strings[i], lengths[i], result.begin() + offset);
        offset += lengths[i];
    }
    return result;
}
 
template <size_t N> struct StaticString
{
    char value[N] = {};
    constexpr StaticString() = default;
    constexpr StaticString(const char (&s)[N])  { q20::copy_n(s, N, value); }
    constexpr operator const char *() const     { return value; }
};
 
template <size_t KL, size_t VL> struct StaticMapEntry
{
    StaticString<KL> key = {};
    StaticString<VL> value = {};
    constexpr StaticMapEntry() = default;
    constexpr StaticMapEntry(const char (&k)[KL], const char (&v)[VL])
        : key(k), value(v)
    {}
};
 
template <typename StringExtractor, typename... T>
constexpr auto makeOffsetStringArray(StringExtractor extractString, const T &... entries)
{
    constexpr size_t Count = sizeof...(T);
    constexpr size_t StringLength = (sizeof(extractString(T{})) + ...);
    using MinifiedOffsetType = decltype(QtPrivate::minifyValue<StringLength>());
 
    size_t offset = 0;
    std::array fullOffsetList = { offset += sizeof(extractString(T{}))... };
 
    // prepend zero
    std::array<MinifiedOffsetType, Count + 1> minifiedOffsetList = {};
    q20::transform(fullOffsetList.begin(), fullOffsetList.end(),
                   minifiedOffsetList.begin() + 1,
                   [] (auto e) { return MinifiedOffsetType(e); });
 
    std::array staticString = QtPrivate::makeStaticString<StringLength>(extractString, entries...);
    return QOffsetStringArray(staticString, minifiedOffsetList);
}
} // namespace QtPrivate
 
template<int ... Nx>
constexpr auto qOffsetStringArray(const char (&...strings)[Nx]) noexcept
{
    auto extractString = [](const auto &s) -> decltype(auto) { return s; };
    return QtPrivate::makeOffsetStringArray(extractString, QtPrivate::StaticString(strings)...);
}
 
QT_WARNING_POP
QT_END_NAMESPACE
 
#endif // QOFFSETSTRINGARRAY_P_H