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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 <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; }
private:
StaticString m_string;
OffsetList m_offsets;
friend tst_QOffsetStringArray;
};
namespace QtPrivate {
// std::copy is not constexpr in C++17
template <typename II, typename OO>
static constexpr OO copyData(II input, qsizetype n, OO output)
{
using E = decltype(+*output);
for (qsizetype i = 0; i < n; ++i)
output[i] = E(input[i]);
return output + n;
}
template <size_t Highest> constexpr auto minifyValue()
{
if constexpr (Highest <= (std::numeric_limits<quint8>::max)()) {
return quint8(Highest);
} else if constexpr (Highest <= (std::numeric_limits<quint16>::max)()) {
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) {
copyData(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]) { copyData(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 qOffsetStringArray(StringExtractor extractString, const T &... entries)
{
constexpr size_t Count = sizeof...(T);
constexpr qsizetype 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 = {};
QtPrivate::copyData(fullOffsetList.begin(), Count, minifiedOffsetList.begin() + 1);
std::array staticString = QtPrivate::makeStaticString<StringLength>(extractString, entries...);
return QOffsetStringArray(staticString, minifiedOffsetList);
}
}
template<int ... Nx>
constexpr auto qOffsetStringArray(const char (&...strings)[Nx]) noexcept
{
auto extractString = [](const auto &s) -> decltype(auto) { return s; };
return QtPrivate::qOffsetStringArray(extractString, QtPrivate::StaticString(strings)...);
}
QT_WARNING_POP
QT_END_NAMESPACE
#endif // QOFFSETSTRINGARRAY_P_H
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