qstringconverter.cpp

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#include <qstringconverter.h>
#include <private/qstringconverter_p.h>
#include "qendian.h"
 
#include "private/qsimd_p.h"
#include "private/qstringiterator_p.h"
#include "private/qtools_p.h"
#include "qbytearraymatcher.h"
 
#ifdef Q_OS_WIN
#include <qt_windows.h>
#ifndef QT_BOOTSTRAPPED
#include <QtCore/qvarlengtharray.h>
#endif // !QT_BOOTSTRAPPED
#endif
 
#if __has_include(<bit>) && __cplusplus > 201703L
#include <bit>
#endif
 
QT_BEGIN_NAMESPACE
 
enum { Endian = 0, Data = 1 };
 
static const uchar utf8bom[] = { 0xef, 0xbb, 0xbf };
 
#if (defined(__SSE2__) && defined(QT_COMPILER_SUPPORTS_SSE2)) \
    || defined(__ARM_NEON__)
static Q_ALWAYS_INLINE uint qBitScanReverse(unsigned v) noexcept
{
#if defined(__cpp_lib_int_pow2) && __cpp_lib_int_pow2 >= 202002L
     return std::bit_width(v) - 1;
#else
    uint result = qCountLeadingZeroBits(v);
    // Now Invert the result: clz will count *down* from the msb to the lsb, so the msb index is 31
    // and the lsb index is 0. The result for _bit_scan_reverse is expected to be the index when
    // counting up: msb index is 0 (because it starts there), and the lsb index is 31.
    result ^= sizeof(unsigned) * 8 - 1;
    return result;
#endif
}
#endif
 
#if defined(__SSE2__) && defined(QT_COMPILER_SUPPORTS_SSE2)
static inline bool simdEncodeAscii(uchar *&dst, const char16_t *&nextAscii, const char16_t *&src, const char16_t *end)
{
    // do sixteen characters at a time
    for ( ; end - src >= 16; src += 16, dst += 16) {
#  ifdef __AVX2__
        __m256i data = _mm256_loadu_si256(reinterpret_cast<const __m256i *>(src));
        __m128i data1 = _mm256_castsi256_si128(data);
        __m128i data2 = _mm256_extracti128_si256(data, 1);
#  else
        __m128i data1 = _mm_loadu_si128((const __m128i*)src);
        __m128i data2 = _mm_loadu_si128(1+(const __m128i*)src);
#  endif
 
        // check if everything is ASCII
        // the highest ASCII value is U+007F
        // Do the packing directly:
        // The PACKUSWB instruction has packs a signed 16-bit integer to an unsigned 8-bit
        // with saturation. That is, anything from 0x0100 to 0x7fff is saturated to 0xff,
        // while all negatives (0x8000 to 0xffff) get saturated to 0x00. To detect non-ASCII,
        // we simply do a signed greater-than comparison to 0x00. That means we detect NULs as
        // "non-ASCII", but it's an acceptable compromise.
        __m128i packed = _mm_packus_epi16(data1, data2);
        __m128i nonAscii = _mm_cmpgt_epi8(packed, _mm_setzero_si128());
 
        // store, even if there are non-ASCII characters here
        _mm_storeu_si128((__m128i*)dst, packed);
 
        // n will contain 1 bit set per character in [data1, data2] that is non-ASCII (or NUL)
        ushort n = ~_mm_movemask_epi8(nonAscii);
        if (n) {
            // find the next probable ASCII character
            // we don't want to load 32 bytes again in this loop if we know there are non-ASCII
            // characters still coming
            nextAscii = src + qBitScanReverse(n) + 1;
 
            n = qCountTrailingZeroBits(n);
            dst += n;
            src += n;
            return false;
        }
    }
 
    if (end - src >= 8) {
        // do eight characters at a time
        __m128i data = _mm_loadu_si128(reinterpret_cast<const __m128i *>(src));
        __m128i packed = _mm_packus_epi16(data, data);
        __m128i nonAscii = _mm_cmpgt_epi8(packed, _mm_setzero_si128());
 
        // store even non-ASCII
        _mm_storel_epi64(reinterpret_cast<__m128i *>(dst), packed);
 
        uchar n = ~_mm_movemask_epi8(nonAscii);
        if (n) {
            nextAscii = src + qBitScanReverse(n) + 1;
            n = qCountTrailingZeroBits(n);
            dst += n;
            src += n;
            return false;
        }
    }
 
    return src == end;
}
 
static inline bool simdDecodeAscii(char16_t *&dst, const uchar *&nextAscii, const uchar *&src, const uchar *end)
{
    // do sixteen characters at a time
    for ( ; end - src >= 16; src += 16, dst += 16) {
        __m128i data = _mm_loadu_si128((const __m128i*)src);
 
#ifdef __AVX2__
        const int BitSpacing = 2;
        // load and zero extend to an YMM register
        const __m256i extended = _mm256_cvtepu8_epi16(data);
 
        uint n = _mm256_movemask_epi8(extended);
        if (!n) {
            // store
            _mm256_storeu_si256((__m256i*)dst, extended);
            continue;
        }
#else
        const int BitSpacing = 1;
 
        // check if everything is ASCII
        // movemask extracts the high bit of every byte, so n is non-zero if something isn't ASCII
        uint n = _mm_movemask_epi8(data);
        if (!n) {
            // unpack
            _mm_storeu_si128((__m128i*)dst, _mm_unpacklo_epi8(data, _mm_setzero_si128()));
            _mm_storeu_si128(1+(__m128i*)dst, _mm_unpackhi_epi8(data, _mm_setzero_si128()));
            continue;
        }
#endif
 
        // copy the front part that is still ASCII
        while (!(n & 1)) {
            *dst++ = *src++;
            n >>= BitSpacing;
        }
 
        // find the next probable ASCII character
        // we don't want to load 16 bytes again in this loop if we know there are non-ASCII
        // characters still coming
        n = qBitScanReverse(n);
        nextAscii = src + (n / BitSpacing) + 1;
        return false;
 
    }
 
    if (end - src >= 8) {
        __m128i data = _mm_loadl_epi64(reinterpret_cast<const __m128i *>(src));
        uint n = _mm_movemask_epi8(data) & 0xff;
        if (!n) {
            // unpack and store
            _mm_storeu_si128(reinterpret_cast<__m128i *>(dst), _mm_unpacklo_epi8(data, _mm_setzero_si128()));
        } else {
            while (!(n & 1)) {
                *dst++ = *src++;
                n >>= 1;
            }
 
            n = qBitScanReverse(n);
            nextAscii = src + n + 1;
            return false;
        }
    }
 
    return src == end;
}
 
static inline const uchar *simdFindNonAscii(const uchar *src, const uchar *end, const uchar *&nextAscii)
{
#ifdef __AVX2__
    // do 32 characters at a time
    // (this is similar to simdTestMask in qstring.cpp)
    const __m256i mask = _mm256_set1_epi8(0x80);
    for ( ; end - src >= 32; src += 32) {
        __m256i data = _mm256_loadu_si256(reinterpret_cast<const __m256i *>(src));
        if (_mm256_testz_si256(mask, data))
            continue;
 
        uint n = _mm256_movemask_epi8(data);
        Q_ASSUME(n);
 
        // find the next probable ASCII character
        // we don't want to load 32 bytes again in this loop if we know there are non-ASCII
        // characters still coming
        nextAscii = src + qBitScanReverse(n) + 1;
 
        // return the non-ASCII character
        return src + qCountTrailingZeroBits(n);
    }
#endif
 
    // do sixteen characters at a time
    for ( ; end - src >= 16; src += 16) {
        __m128i data = _mm_loadu_si128(reinterpret_cast<const __m128i*>(src));
 
        // check if everything is ASCII
        // movemask extracts the high bit of every byte, so n is non-zero if something isn't ASCII
        uint n = _mm_movemask_epi8(data);
        if (!n)
            continue;
 
        // find the next probable ASCII character
        // we don't want to load 16 bytes again in this loop if we know there are non-ASCII
        // characters still coming
        nextAscii = src + qBitScanReverse(n) + 1;
 
        // return the non-ASCII character
        return src + qCountTrailingZeroBits(n);
    }
 
    // do four characters at a time
    for ( ; end - src >= 4; src += 4) {
        quint32 data = qFromUnaligned<quint32>(src);
        data &= 0x80808080U;
        if (!data)
            continue;
 
        // We don't try to guess which of the three bytes is ASCII and which
        // one isn't. The chance that at least two of them are non-ASCII is
        // better than 75%.
        nextAscii = src;
        return src;
    }
    nextAscii = end;
    return src;
}
 
// Compare only the US-ASCII beginning of [src8, end8) and [src16, end16)
// and advance src8 and src16 to the first character that could not be compared
static void simdCompareAscii(const char8_t *&src8, const char8_t *end8, const char16_t *&src16, const char16_t *end16)
{
    int bitSpacing = 1;
    qptrdiff len = qMin(end8 - src8, end16 - src16);
    qptrdiff offset = 0;
    uint mask = 0;
 
    // do sixteen characters at a time
    for ( ; offset + 16 < len; offset += 16) {
        __m128i data8 = _mm_loadu_si128(reinterpret_cast<const __m128i *>(src8 + offset));
#ifdef __AVX2__
        // AVX2 version, use 256-bit registers and VPMOVXZBW
        __m256i data16 = _mm256_loadu_si256(reinterpret_cast<const __m256i *>(src16 + offset));
 
        // expand US-ASCII as if it were Latin1 and confirm it's US-ASCII
        __m256i datax8 = _mm256_cvtepu8_epi16(data8);
        mask = _mm256_movemask_epi8(datax8);
        if (mask)
            break;
 
        // compare Latin1 to UTF-16
        __m256i latin1cmp = _mm256_cmpeq_epi16(datax8, data16);
        mask = ~_mm256_movemask_epi8(latin1cmp);
        if (mask)
            break;
#else
        // non-AVX2 code
        __m128i datalo16 = _mm_loadu_si128(reinterpret_cast<const __m128i *>(src16 + offset));
        __m128i datahi16 = _mm_loadu_si128(reinterpret_cast<const __m128i *>(src16 + offset) + 1);
 
        // expand US-ASCII as if it were Latin1, we'll confirm later
        __m128i datalo8 = _mm_unpacklo_epi8(data8, _mm_setzero_si128());
        __m128i datahi8 = _mm_unpackhi_epi8(data8, _mm_setzero_si128());
 
        // compare Latin1 to UTF-16
        __m128i latin1cmplo = _mm_cmpeq_epi16(datalo8, datalo16);
        __m128i latin1cmphi = _mm_cmpeq_epi16(datahi8, datahi16);
        mask = _mm_movemask_epi8(latin1cmphi) << 16;
        mask |= ushort(_mm_movemask_epi8(latin1cmplo));
        mask = ~mask;
        if (mask)
            break;
 
        // confirm it was US-ASCII
        mask = _mm_movemask_epi8(data8);
        if (mask) {
            bitSpacing = 0;
            break;
        }
#endif
    }
 
    // helper for comparing 4 or 8 characters
    auto cmp_lt_16 = [&mask, &offset](int n, __m128i data8, __m128i data16) {
        // n = 4  ->  sizemask = 0xff
        // n = 8  ->  sizemask = 0xffff
        unsigned sizemask = (1U << (2 * n)) - 1;
 
        // expand as if Latin1
        data8 = _mm_unpacklo_epi8(data8, _mm_setzero_si128());
 
        // compare and confirm it's US-ASCII
        __m128i latin1cmp = _mm_cmpeq_epi16(data8, data16);
        mask = ~_mm_movemask_epi8(latin1cmp) & sizemask;
        mask |= _mm_movemask_epi8(data8);
        if (mask == 0)
            offset += n;
    };
 
    // do eight characters at a time
    if (mask == 0 && offset + 8 < len) {
        __m128i data8 = _mm_loadl_epi64(reinterpret_cast<const __m128i *>(src8 + offset));
        __m128i data16 = _mm_loadu_si128(reinterpret_cast<const __m128i *>(src16 + offset));
        cmp_lt_16(8, data8, data16);
    }
 
    // do four characters
    if (mask == 0 && offset + 4 < len) {
        __m128i data8 = _mm_cvtsi32_si128(qFromUnaligned<quint32>(src8 + offset));
        __m128i data16 = _mm_loadl_epi64(reinterpret_cast<const __m128i *>(src16 + offset));
        cmp_lt_16(4, data8, data16);
    }
 
    // correct the source pointers to point to the first character we couldn't deal with
    if (mask)
        offset += qCountTrailingZeroBits(mask) >> bitSpacing;
    src8 += offset;
    src16 += offset;
}
#elif defined(__ARM_NEON__)
static inline bool simdEncodeAscii(uchar *&dst, const char16_t *&nextAscii, const char16_t *&src, const char16_t *end)
{
    uint16x8_t maxAscii = vdupq_n_u16(0x7f);
    uint16x8_t mask1 = { 1,      1 << 2, 1 << 4, 1 << 6, 1 << 8, 1 << 10, 1 << 12, 1 << 14 };
    uint16x8_t mask2 = vshlq_n_u16(mask1, 1);
 
    // do sixteen characters at a time
    for ( ; end - src >= 16; src += 16, dst += 16) {
        // load 2 lanes (or: "load interleaved")
        uint16x8x2_t in = vld2q_u16(reinterpret_cast<const uint16_t *>(src));
 
        // check if any of the elements > 0x7f, select 1 bit per element (element 0 -> bit 0, element 1 -> bit 1, etc),
        // add those together into a scalar, and merge the scalars.
        uint16_t nonAscii = vaddvq_u16(vandq_u16(vcgtq_u16(in.val[0], maxAscii), mask1))
                          | vaddvq_u16(vandq_u16(vcgtq_u16(in.val[1], maxAscii), mask2));
 
        // merge the two lanes by shifting the values of the second by 8 and inserting them
        uint16x8_t out = vsliq_n_u16(in.val[0], in.val[1], 8);
 
        // store, even if there are non-ASCII characters here
        vst1q_u8(dst, vreinterpretq_u8_u16(out));
 
        if (nonAscii) {
            // find the next probable ASCII character
            // we don't want to load 32 bytes again in this loop if we know there are non-ASCII
            // characters still coming
            nextAscii = src + qBitScanReverse(nonAscii) + 1;
 
            nonAscii = qCountTrailingZeroBits(nonAscii);
            dst += nonAscii;
            src += nonAscii;
            return false;
        }
    }
    return src == end;
}
 
static inline bool simdDecodeAscii(char16_t *&dst, const uchar *&nextAscii, const uchar *&src, const uchar *end)
{
    // do eight characters at a time
    uint8x8_t msb_mask = vdup_n_u8(0x80);
    uint8x8_t add_mask = { 1, 1 << 1, 1 << 2, 1 << 3, 1 << 4, 1 << 5, 1 << 6, 1 << 7 };
    for ( ; end - src >= 8; src += 8, dst += 8) {
        uint8x8_t c = vld1_u8(src);
        uint8_t n = vaddv_u8(vand_u8(vcge_u8(c, msb_mask), add_mask));
        if (!n) {
            // store
            vst1q_u16(reinterpret_cast<uint16_t *>(dst), vmovl_u8(c));
            continue;
        }
 
        // copy the front part that is still ASCII
        while (!(n & 1)) {
            *dst++ = *src++;
            n >>= 1;
        }
 
        // find the next probable ASCII character
        // we don't want to load 16 bytes again in this loop if we know there are non-ASCII
        // characters still coming
        n = qBitScanReverse(n);
        nextAscii = src + n + 1;
        return false;
 
    }
    return src == end;
}
 
static inline const uchar *simdFindNonAscii(const uchar *src, const uchar *end, const uchar *&nextAscii)
{
    // The SIMD code below is untested, so just force an early return until
    // we've had the time to verify it works.
    nextAscii = end;
    return src;
 
    // do eight characters at a time
    uint8x8_t msb_mask = vdup_n_u8(0x80);
    uint8x8_t add_mask = { 1, 1 << 1, 1 << 2, 1 << 3, 1 << 4, 1 << 5, 1 << 6, 1 << 7 };
    for ( ; end - src >= 8; src += 8) {
        uint8x8_t c = vld1_u8(src);
        uint8_t n = vaddv_u8(vand_u8(vcge_u8(c, msb_mask), add_mask));
        if (!n)
            continue;
 
        // find the next probable ASCII character
        // we don't want to load 16 bytes again in this loop if we know there are non-ASCII
        // characters still coming
        nextAscii = src + qBitScanReverse(n) + 1;
 
        // return the non-ASCII character
        return src + qCountTrailingZeroBits(n);
    }
    nextAscii = end;
    return src;
}
 
static void simdCompareAscii(const char8_t *&, const char8_t *, const char16_t *&, const char16_t *)
{
}
#else
static inline bool simdEncodeAscii(uchar *, const char16_t *, const char16_t *, const char16_t *)
{
    return false;
}
 
static inline bool simdDecodeAscii(char16_t *, const uchar *, const uchar *, const uchar *)
{
    return false;
}
 
static inline const uchar *simdFindNonAscii(const uchar *src, const uchar *end, const uchar *&nextAscii)
{
    nextAscii = end;
    return src;
}
 
static void simdCompareAscii(const char8_t *&, const char8_t *, const char16_t *&, const char16_t *)
{
}
#endif
 
enum { HeaderDone = 1 };
 
QByteArray QUtf8::convertFromUnicode(QStringView in)
{
    qsizetype len = in.size();
 
    // create a QByteArray with the worst case scenario size
    QByteArray result(len * 3, Qt::Uninitialized);
    uchar *dst = reinterpret_cast<uchar *>(const_cast<char *>(result.constData()));
    const char16_t *src = reinterpret_cast<const char16_t *>(in.data());
    const char16_t *const end = src + len;
 
    while (src != end) {
        const char16_t *nextAscii = end;
        if (simdEncodeAscii(dst, nextAscii, src, end))
            break;
 
        do {
            char16_t u = *src++;
            int res = QUtf8Functions::toUtf8<QUtf8BaseTraits>(u, dst, src, end);
            if (res < 0) {
                // encoding error - append '?'
                *dst++ = '?';
            }
        } while (src < nextAscii);
    }
 
    result.truncate(dst - reinterpret_cast<uchar *>(const_cast<char *>(result.constData())));
    return result;
}
 
QByteArray QUtf8::convertFromUnicode(QStringView in, QStringConverterBase::State *state)
{
    QByteArray ba(3*in.size() +3, Qt::Uninitialized);
    char *end = convertFromUnicode(ba.data(), in, state);
    ba.truncate(end - ba.data());
    return ba;
}
 
char *QUtf8::convertFromUnicode(char *out, QStringView in, QStringConverter::State *state)
{
    Q_ASSERT(state);
    const QChar *uc = in.data();
    qsizetype len = in.length();
    if (!len)
        return out;
 
    auto appendReplacementChar = [state](uchar *cursor) -> uchar * {
        if (state->flags & QStringConverter::Flag::ConvertInvalidToNull) {
            *cursor++ = 0;
        } else {
            // QChar::replacement encoded in utf8
            *cursor++ = 0xef;
            *cursor++ = 0xbf;
            *cursor++ = 0xbd;
        }
        return cursor;
    };
 
    uchar *cursor = reinterpret_cast<uchar *>(out);
    const char16_t *src = reinterpret_cast<const char16_t *>(uc);
    const char16_t *const end = src + len;
 
    if (!(state->flags & QStringDecoder::Flag::Stateless)) {
        if (state->remainingChars) {
            int res = QUtf8Functions::toUtf8<QUtf8BaseTraits>(state->state_data[0], cursor, src, end);
            if (res < 0)
                cursor = appendReplacementChar(cursor);
            state->state_data[0] = 0;
            state->remainingChars = 0;
        } else if (!(state->internalState & HeaderDone) && state->flags & QStringConverter::Flag::WriteBom) {
            // append UTF-8 BOM
            *cursor++ = utf8bom[0];
            *cursor++ = utf8bom[1];
            *cursor++ = utf8bom[2];
            state->internalState |= HeaderDone;
        }
    }
 
    while (src != end) {
        const char16_t *nextAscii = end;
        if (simdEncodeAscii(cursor, nextAscii, src, end))
            break;
 
        do {
            char16_t uc = *src++;
            int res = QUtf8Functions::toUtf8<QUtf8BaseTraits>(uc, cursor, src, end);
            if (Q_LIKELY(res >= 0))
                continue;
 
            if (res == QUtf8BaseTraits::Error) {
                // encoding error
                ++state->invalidChars;
                cursor = appendReplacementChar(cursor);
            } else if (res == QUtf8BaseTraits::EndOfString) {
                if (state->flags & QStringConverter::Flag::Stateless) {
                    ++state->invalidChars;
                    cursor = appendReplacementChar(cursor);
                } else {
                    state->remainingChars = 1;
                    state->state_data[0] = uc;
                }
                return reinterpret_cast<char *>(cursor);
            }
        } while (src < nextAscii);
    }
 
    return reinterpret_cast<char *>(cursor);
}
 
QString QUtf8::convertToUnicode(QByteArrayView in)
{
    // UTF-8 to UTF-16 always needs the exact same number of words or less:
    //    UTF-8     UTF-16
    //   1 byte     1 word
    //   2 bytes    1 word
    //   3 bytes    1 word
    //   4 bytes    2 words (one surrogate pair)
    // That is, we'll use the full buffer if the input is US-ASCII (1-byte UTF-8),
    // half the buffer for U+0080-U+07FF text (e.g., Greek, Cyrillic, Arabic) or
    // non-BMP text, and one third of the buffer for U+0800-U+FFFF text (e.g, CJK).
    //
    // The table holds for invalid sequences too: we'll insert one replacement char
    // per invalid byte.
    QString result(in.size(), Qt::Uninitialized);
    QChar *data = const_cast<QChar*>(result.constData()); // we know we're not shared
    const QChar *end = convertToUnicode(data, in);
    result.truncate(end - data);
    return result;
}
 
QChar *QUtf8::convertToUnicode(QChar *buffer, QByteArrayView in) noexcept
{
    char16_t *dst = reinterpret_cast<char16_t *>(buffer);
    const uchar *const start = reinterpret_cast<const uchar *>(in.data());
    const uchar *src = start;
    const uchar *end = src + in.size();
 
    // attempt to do a full decoding in SIMD
    const uchar *nextAscii = end;
    if (!simdDecodeAscii(dst, nextAscii, src, end)) {
        // at least one non-ASCII entry
        // check if we failed to decode the UTF-8 BOM; if so, skip it
        if (Q_UNLIKELY(src == start)
                && end - src >= 3
                && Q_UNLIKELY(src[0] == utf8bom[0] && src[1] == utf8bom[1] && src[2] == utf8bom[2])) {
            src += 3;
        }
 
        while (src < end) {
            nextAscii = end;
            if (simdDecodeAscii(dst, nextAscii, src, end))
                break;
 
            do {
                uchar b = *src++;
                int res = QUtf8Functions::fromUtf8<QUtf8BaseTraits>(b, dst, src, end);
                if (res < 0) {
                    // decoding error
                    *dst++ = QChar::ReplacementCharacter;
                }
            } while (src < nextAscii);
        }
    }
 
    return reinterpret_cast<QChar *>(dst);
}
 
QString QUtf8::convertToUnicode(QByteArrayView in, QStringConverter::State *state)
{
    // See above for buffer requirements for stateless decoding. However, that
    // fails if the state is not empty. The following situations can add to the
    // requirements:
    //  state contains      chars starts with           requirement
    //   1 of 2 bytes       valid continuation          0
    //   2 of 3 bytes       same                        0
    //   3 bytes of 4       same                        +1 (need to insert surrogate pair)
    //   1 of 2 bytes       invalid continuation        +1 (need to insert replacement and restart)
    //   2 of 3 bytes       same                        +1 (same)
    //   3 of 4 bytes       same                        +1 (same)
    QString result(in.size() + 1, Qt::Uninitialized);
    QChar *end = convertToUnicode(result.data(), in, state);
    result.truncate(end - result.constData());
    return result;
}
 
QChar *QUtf8::convertToUnicode(QChar *out, QByteArrayView in, QStringConverter::State *state)
{
    qsizetype len = in.size();
 
    Q_ASSERT(state);
    if (!len)
        return out;
 
 
    char16_t replacement = QChar::ReplacementCharacter;
    if (state->flags & QStringConverter::Flag::ConvertInvalidToNull)
        replacement = QChar::Null;
 
    int res;
    uchar ch = 0;
 
    char16_t *dst = reinterpret_cast<char16_t *>(out);
    const uchar *src = reinterpret_cast<const uchar *>(in.data());
    const uchar *end = src + len;
 
    if (!(state->flags & QStringConverter::Flag::Stateless)) {
        bool headerdone = state->internalState & HeaderDone || state->flags & QStringConverter::Flag::ConvertInitialBom;
        if (state->remainingChars || !headerdone) {
            // handle incoming state first
            uchar remainingCharsData[4]; // longest UTF-8 sequence possible
            qsizetype remainingCharsCount = state->remainingChars;
            qsizetype newCharsToCopy = qMin<qsizetype>(sizeof(remainingCharsData) - remainingCharsCount, end - src);
 
            memset(remainingCharsData, 0, sizeof(remainingCharsData));
            memcpy(remainingCharsData, &state->state_data[0], remainingCharsCount);
            memcpy(remainingCharsData + remainingCharsCount, src, newCharsToCopy);
 
            const uchar *begin = &remainingCharsData[1];
            res = QUtf8Functions::fromUtf8<QUtf8BaseTraits>(remainingCharsData[0], dst, begin,
                    static_cast<const uchar *>(remainingCharsData) + remainingCharsCount + newCharsToCopy);
            if (res == QUtf8BaseTraits::Error) {
                ++state->invalidChars;
                *dst++ = replacement;
                ++src;
            } else if (res == QUtf8BaseTraits::EndOfString) {
                // if we got EndOfString again, then there were too few bytes in src;
                // copy to our state and return
                state->remainingChars = remainingCharsCount + newCharsToCopy;
                memcpy(&state->state_data[0], remainingCharsData, state->remainingChars);
                return out;
            } else if (!headerdone) {
                // eat the UTF-8 BOM
                if (dst[-1] == 0xfeff)
                    --dst;
            }
            state->internalState |= HeaderDone;
 
            // adjust src now that we have maybe consumed a few chars
            if (res >= 0) {
                Q_ASSERT(res > remainingCharsCount);
                src += res - remainingCharsCount;
            }
        }
    } else if (!(state->flags & QStringConverter::Flag::ConvertInitialBom)) {
        // stateless, remove initial BOM
        if (len > 2 && src[0] == utf8bom[0] && src[1] == utf8bom[1] && src[2] == utf8bom[2])
            // skip BOM
            src += 3;
    }
 
    // main body, stateless decoding
    res = 0;
    const uchar *nextAscii = src;
    while (res >= 0 && src < end) {
        if (src >= nextAscii && simdDecodeAscii(dst, nextAscii, src, end))
            break;
 
        ch = *src++;
        res = QUtf8Functions::fromUtf8<QUtf8BaseTraits>(ch, dst, src, end);
        if (res == QUtf8BaseTraits::Error) {
            res = 0;
            ++state->invalidChars;
            *dst++ = replacement;
        }
    }
 
    if (res == QUtf8BaseTraits::EndOfString) {
        // unterminated UTF sequence
        if (state->flags & QStringConverter::Flag::Stateless) {
            *dst++ = QChar::ReplacementCharacter;
            ++state->invalidChars;
            while (src++ < end) {
                *dst++ = QChar::ReplacementCharacter;
                ++state->invalidChars;
            }
            state->remainingChars = 0;
        } else {
            --src; // unread the byte in ch
            state->remainingChars = end - src;
            memcpy(&state->state_data[0], src, end - src);
        }
    } else {
        state->remainingChars = 0;
    }
 
    return reinterpret_cast<QChar *>(dst);
}
 
struct QUtf8NoOutputTraits : public QUtf8BaseTraitsNoAscii
{
    struct NoOutput {};
    static void appendUtf16(const NoOutput &, char16_t) {}
    static void appendUcs4(const NoOutput &, char32_t) {}
};
 
QUtf8::ValidUtf8Result QUtf8::isValidUtf8(QByteArrayView in)
{
    const uchar *src = reinterpret_cast<const uchar *>(in.data());
    const uchar *end = src + in.size();
    const uchar *nextAscii = src;
    bool isValidAscii = true;
 
    while (src < end) {
        if (src >= nextAscii)
            src = simdFindNonAscii(src, end, nextAscii);
        if (src == end)
            break;
 
        do {
            uchar b = *src++;
            if ((b & 0x80) == 0)
                continue;
 
            isValidAscii = false;
            QUtf8NoOutputTraits::NoOutput output;
            int res = QUtf8Functions::fromUtf8<QUtf8NoOutputTraits>(b, output, src, end);
            if (res < 0) {
                // decoding error
                return { false, false };
            }
        } while (src < nextAscii);
    }
 
    return { true, isValidAscii };
}
 
int QUtf8::compareUtf8(QByteArrayView utf8, QStringView utf16) noexcept
{
    auto src1 = reinterpret_cast<const char8_t *>(utf8.data());
    auto end1 = src1 + utf8.size();
    auto src2 = reinterpret_cast<const char16_t *>(utf16.data());
    auto end2 = src2 + utf16.size();
 
    do {
        simdCompareAscii(src1, end1, src2, end2);
 
        if (src1 < end1 && src2 < end2) {
            char32_t uc1 = *src1++;
            char32_t uc2 = *src2++;
 
            if (uc1 >= 0x80) {
                char32_t *output = &uc1;
                int res = QUtf8Functions::fromUtf8<QUtf8BaseTraitsNoAscii>(uc1, output, src1, end1);
                if (res < 0) {
                    // decoding error
                    uc1 = QChar::ReplacementCharacter;
                }
 
                // Only decode the UTF-16 surrogate pair if the UTF-8 code point
                // wasn't US-ASCII (a surrogate cannot match US-ASCII).
                if (QChar::isHighSurrogate(uc2) && src2 < end2 && QChar::isLowSurrogate(*src2))
                    uc2 = QChar::surrogateToUcs4(uc2, *src2++);
            }
 
            if (uc1 != uc2)
                return int(uc1) - int(uc2);
        }
    } while (src1 < end1 && src2 < end2);
 
    // the shorter string sorts first
    return (end1 > src1) - int(end2 > src2);
}
 
int QUtf8::compareUtf8(QByteArrayView utf8, QLatin1String s)
{
    char32_t uc1 = QChar::Null;
    auto src1 = reinterpret_cast<const uchar *>(utf8.data());
    auto end1 = src1 + utf8.size();
    auto src2 = reinterpret_cast<const uchar *>(s.latin1());
    auto end2 = src2 + s.size();
 
    while (src1 < end1 && src2 < end2) {
        uchar b = *src1++;
        char32_t *output = &uc1;
        int res = QUtf8Functions::fromUtf8<QUtf8BaseTraits>(b, output, src1, end1);
        if (res < 0) {
            // decoding error
            uc1 = QChar::ReplacementCharacter;
        }
 
        char32_t uc2 = *src2++;
        if (uc1 != uc2)
            return int(uc1) - int(uc2);
    }
 
    // the shorter string sorts first
    return (end1 > src1) - (end2 > src2);
}
 
QByteArray QUtf16::convertFromUnicode(QStringView in, QStringConverter::State *state, DataEndianness endian)
{
    bool writeBom = !(state->internalState & HeaderDone) && state->flags & QStringConverter::Flag::WriteBom;
    qsizetype length = 2 * in.size();
    if (writeBom)
        length += 2;
 
    QByteArray d(length, Qt::Uninitialized);
    char *end = convertFromUnicode(d.data(), in, state, endian);
    Q_ASSERT(end - d.constData() == d.length());
    Q_UNUSED(end);
    return d;
}
 
char *QUtf16::convertFromUnicode(char *out, QStringView in, QStringConverter::State *state, DataEndianness endian)
{
    Q_ASSERT(state);
    bool writeBom = !(state->internalState & HeaderDone) && state->flags & QStringConverter::Flag::WriteBom;
 
    if (endian == DetectEndianness)
        endian = (QSysInfo::ByteOrder == QSysInfo::BigEndian) ? BigEndianness : LittleEndianness;
 
    if (writeBom) {
        // set them up the BOM
        QChar bom(QChar::ByteOrderMark);
        if (endian == BigEndianness)
            qToBigEndian(bom.unicode(), out);
        else
            qToLittleEndian(bom.unicode(), out);
        out += 2;
    }
    if (endian == BigEndianness)
        qToBigEndian<char16_t>(in.data(), in.length(), out);
    else
        qToLittleEndian<char16_t>(in.data(), in.length(), out);
 
    state->remainingChars = 0;
    state->internalState |= HeaderDone;
    return out + 2*in.length();
}
 
QString QUtf16::convertToUnicode(QByteArrayView in, QStringConverter::State *state, DataEndianness endian)
{
    QString result((in.size() + 1) >> 1, Qt::Uninitialized); // worst case
    QChar *qch = convertToUnicode(result.data(), in, state, endian);
    result.truncate(qch - result.constData());
    return result;
}
 
QChar *QUtf16::convertToUnicode(QChar *out, QByteArrayView in, QStringConverter::State *state, DataEndianness endian)
{
    qsizetype len = in.size();
    const char *chars = in.data();
 
    Q_ASSERT(state);
 
    if (endian == DetectEndianness)
        endian = (DataEndianness)state->state_data[Endian];
 
    const char *end = chars + len;
 
    // make sure we can decode at least one char
    if (state->remainingChars + len < 2) {
        if (len) {
            Q_ASSERT(state->remainingChars == 0 && len == 1);
            state->remainingChars = 1;
            state->state_data[Data] = *chars;
        }
        return out;
    }
 
    bool headerdone = state && state->internalState & HeaderDone;
    if (state->flags & QStringConverter::Flag::ConvertInitialBom)
        headerdone = true;
 
    if (!headerdone || state->remainingChars) {
        uchar buf;
        if (state->remainingChars)
            buf = state->state_data[Data];
        else
            buf = *chars++;
 
        // detect BOM, set endianness
        state->internalState |= HeaderDone;
        QChar ch(buf, *chars++);
        if (endian == DetectEndianness) {
            // someone set us up the BOM
            if (ch == QChar::ByteOrderSwapped) {
                endian = BigEndianness;
            } else if (ch == QChar::ByteOrderMark) {
                endian = LittleEndianness;
            } else {
                if (QSysInfo::ByteOrder == QSysInfo::BigEndian) {
                    endian = BigEndianness;
                } else {
                    endian = LittleEndianness;
                }
            }
        }
        if (endian == BigEndianness)
            ch = QChar::fromUcs2((ch.unicode() >> 8) | ((ch.unicode() & 0xff) << 8));
        if (headerdone || ch != QChar::ByteOrderMark)
            *out++ = ch;
    } else if (endian == DetectEndianness) {
        endian = (QSysInfo::ByteOrder == QSysInfo::BigEndian) ? BigEndianness : LittleEndianness;
    }
 
    qsizetype nPairs = (end - chars) >> 1;
    if (endian == BigEndianness)
        qFromBigEndian<char16_t>(chars, nPairs, out);
    else
        qFromLittleEndian<char16_t>(chars, nPairs, out);
    out += nPairs;
 
    state->state_data[Endian] = endian;
    state->remainingChars = 0;
    if ((end - chars) & 1) {
        if (state->flags & QStringConverter::Flag::Stateless) {
            *out++ = state->flags & QStringConverter::Flag::ConvertInvalidToNull ? QChar::Null : QChar::ReplacementCharacter;
        } else {
            state->remainingChars = 1;
            state->state_data[Data] = *(end - 1);
        }
    } else {
        state->state_data[Data] = 0;
    }
 
    return out;
}
 
QByteArray QUtf32::convertFromUnicode(QStringView in, QStringConverter::State *state, DataEndianness endian)
{
    bool writeBom = !(state->internalState & HeaderDone) && state->flags & QStringConverter::Flag::WriteBom;
    qsizetype length =  4*in.size();
    if (writeBom)
        length += 4;
    QByteArray ba(length, Qt::Uninitialized);
    char *end = convertFromUnicode(ba.data(), in, state, endian);
    ba.truncate(end - ba.constData());
    return ba;
}
 
char *QUtf32::convertFromUnicode(char *out, QStringView in, QStringConverter::State *state, DataEndianness endian)
{
    Q_ASSERT(state);
 
    bool writeBom = !(state->internalState & HeaderDone) && state->flags & QStringConverter::Flag::WriteBom;
    if (endian == DetectEndianness)
        endian = (QSysInfo::ByteOrder == QSysInfo::BigEndian) ? BigEndianness : LittleEndianness;
 
    if (writeBom) {
        // set them up the BOM
        if (endian == BigEndianness) {
            out[0] = 0;
            out[1] = 0;
            out[2] = (char)0xfe;
            out[3] = (char)0xff;
        } else {
            out[0] = (char)0xff;
            out[1] = (char)0xfe;
            out[2] = 0;
            out[3] = 0;
        }
        out += 4;
        state->internalState |= HeaderDone;
    }
 
    const QChar *uc = in.data();
    const QChar *end = in.data() + in.length();
    QChar ch;
    char32_t ucs4;
    if (state->remainingChars == 1) {
        auto character = state->state_data[Data];
        Q_ASSERT(character <= 0xFFFF);
        ch = QChar(character);
        // this is ugly, but shortcuts a whole lot of logic that would otherwise be required
        state->remainingChars = 0;
        goto decode_surrogate;
    }
 
    while (uc < end) {
        ch = *uc++;
        if (Q_LIKELY(!ch.isSurrogate())) {
            ucs4 = ch.unicode();
        } else if (Q_LIKELY(ch.isHighSurrogate())) {
decode_surrogate:
            if (uc == end) {
                if (state->flags & QStringConverter::Flag::Stateless) {
                    ucs4 = state->flags & QStringConverter::Flag::ConvertInvalidToNull ? 0 : QChar::ReplacementCharacter;
                } else {
                    state->remainingChars = 1;
                    state->state_data[Data] = ch.unicode();
                    return out;
                }
            } else if (uc->isLowSurrogate()) {
                ucs4 = QChar::surrogateToUcs4(ch, *uc++);
            } else {
                ucs4 = state->flags & QStringConverter::Flag::ConvertInvalidToNull ? 0 : QChar::ReplacementCharacter;
            }
        } else {
            ucs4 = state->flags & QStringConverter::Flag::ConvertInvalidToNull ? 0 : QChar::ReplacementCharacter;
        }
        if (endian == BigEndianness)
            qToBigEndian(ucs4, out);
        else
            qToLittleEndian(ucs4, out);
        out += 4;
    }
 
    return out;
}
 
QString QUtf32::convertToUnicode(QByteArrayView in, QStringConverter::State *state, DataEndianness endian)
{
    QString result;
    result.resize((in.size() + 7) >> 1); // worst case
    QChar *end = convertToUnicode(result.data(), in, state, endian);
    result.truncate(end - result.constData());
    return result;
}
 
QChar *QUtf32::convertToUnicode(QChar *out, QByteArrayView in, QStringConverter::State *state, DataEndianness endian)
{
    qsizetype len = in.size();
    const char *chars = in.data();
 
    Q_ASSERT(state);
    if (endian == DetectEndianness)
        endian = (DataEndianness)state->state_data[Endian];
 
    const char *end = chars + len;
 
    uchar tuple[4];
    memcpy(tuple, &state->state_data[Data], 4);
 
    // make sure we can decode at least one char
    if (state->remainingChars + len < 4) {
        if (len) {
            while (chars < end) {
                tuple[state->remainingChars] = *chars;
                ++state->remainingChars;
                ++chars;
            }
            Q_ASSERT(state->remainingChars < 4);
            memcpy(&state->state_data[Data], tuple, 4);
        }
        return out;
    }
 
    bool headerdone = state->internalState & HeaderDone;
    if (state->flags & QStringConverter::Flag::ConvertInitialBom)
        headerdone = true;
 
    qsizetype num = state->remainingChars;
    state->remainingChars = 0;
 
    if (!headerdone || endian == DetectEndianness || num) {
        while (num < 4)
            tuple[num++] = *chars++;
        if (endian == DetectEndianness) {
            // someone set us up the BOM?
            if (tuple[0] == 0xff && tuple[1] == 0xfe && tuple[2] == 0 && tuple[3] == 0) {
                endian = LittleEndianness;
            } else if (tuple[0] == 0 && tuple[1] == 0 && tuple[2] == 0xfe && tuple[3] == 0xff) {
                endian = BigEndianness;
            } else if (QSysInfo::ByteOrder == QSysInfo::BigEndian) {
                endian = BigEndianness;
            } else {
                endian = LittleEndianness;
            }
        }
        char32_t code = (endian == BigEndianness) ? qFromBigEndian<char32_t>(tuple) : qFromLittleEndian<char32_t>(tuple);
        if (headerdone || code != QChar::ByteOrderMark) {
            if (QChar::requiresSurrogates(code)) {
                *out++ = QChar(QChar::highSurrogate(code));
                *out++ = QChar(QChar::lowSurrogate(code));
            } else {
                *out++ = QChar(code);
            }
        }
        num = 0;
    } else if (endian == DetectEndianness) {
        endian = (QSysInfo::ByteOrder == QSysInfo::BigEndian) ? BigEndianness : LittleEndianness;
    }
    state->state_data[Endian] = endian;
    state->internalState |= HeaderDone;
 
    while (chars < end) {
        tuple[num++] = *chars++;
        if (num == 4) {
            char32_t code = (endian == BigEndianness) ? qFromBigEndian<char32_t>(tuple) : qFromLittleEndian<char32_t>(tuple);
            for (char16_t c : QChar::fromUcs4(code))
                *out++ = c;
            num = 0;
        }
    }
 
    if (num) {
        if (state->flags & QStringDecoder::Flag::Stateless) {
            *out++ = QChar::ReplacementCharacter;
        } else {
            state->state_data[Endian] = endian;
            state->remainingChars = num;
            memcpy(&state->state_data[Data], tuple, 4);
        }
    }
 
    return out;
}
 
#if defined(Q_OS_WIN) && !defined(QT_BOOTSTRAPPED)
static QString convertToUnicodeCharByChar(QByteArrayView in, QStringConverter::State *state)
{
    qsizetype length = in.size();
    const char *chars = in.data();
 
    Q_ASSERT(state);
    if (state->flags & QStringConverter::Flag::Stateless) // temporary
        state = nullptr;
 
    if (!chars || !length)
        return QString();
 
    qsizetype copyLocation = 0;
    qsizetype extra = 2;
    if (state && state->remainingChars) {
        copyLocation = state->remainingChars;
        extra += copyLocation;
    }
    qsizetype newLength = length + extra;
    char *mbcs = new char[newLength];
    //ensure that we have a NULL terminated string
    mbcs[newLength-1] = 0;
    mbcs[newLength-2] = 0;
    memcpy(&(mbcs[copyLocation]), chars, length);
    if (copyLocation) {
        //copy the last character from the state
        mbcs[0] = (char)state->state_data[0];
        state->remainingChars = 0;
    }
    const char *mb = mbcs;
    const char *next = 0;
    QString s;
    while ((next = CharNextExA(CP_ACP, mb, 0)) != mb) {
        wchar_t wc[2] ={0};
        int charlength = next - mb;
        int len = MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED|MB_ERR_INVALID_CHARS, mb, charlength, wc, 2);
        if (len>0) {
            s.append(QChar(wc[0]));
        } else {
            int r = GetLastError();
            //check if the character being dropped is the last character
            if (r == ERROR_NO_UNICODE_TRANSLATION && mb == (mbcs+newLength -3) && state) {
                state->remainingChars = 1;
                state->state_data[0] = (char)*mb;
            }
        }
        mb = next;
    }
    delete [] mbcs;
    return s;
}
 
 
QString QLocal8Bit::convertToUnicode(QByteArrayView in, QStringConverter::State *state)
{
    qsizetype length = in.size();
 
    Q_ASSERT(length < INT_MAX); // ### FIXME
    const char *mb = in.data();
    int mblen = length;
 
    if (!mb || !mblen)
        return QString();
 
    QVarLengthArray<wchar_t, 4096> wc(4096);
    int len;
    QString sp;
    bool prepend = false;
    char state_data = 0;
    int remainingChars = 0;
 
    //save the current state information
    if (state) {
        state_data = (char)state->state_data[0];
        remainingChars = state->remainingChars;
    }
 
    //convert the pending character (if available)
    if (state && remainingChars) {
        char prev[3] = {0};
        prev[0] = state_data;
        prev[1] = mb[0];
        remainingChars = 0;
        len = MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED,
                                    prev, 2, wc.data(), wc.length());
        if (len) {
            sp.append(QChar(wc[0]));
            if (mblen == 1) {
                state->remainingChars = 0;
                return sp;
            }
            prepend = true;
            mb++;
            mblen--;
            wc[0] = 0;
        }
    }
 
    while (!(len=MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED|MB_ERR_INVALID_CHARS,
                mb, mblen, wc.data(), wc.length()))) {
        int r = GetLastError();
        if (r == ERROR_INSUFFICIENT_BUFFER) {
                const int wclen = MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED,
                                    mb, mblen, 0, 0);
                wc.resize(wclen);
        } else if (r == ERROR_NO_UNICODE_TRANSLATION) {
            //find the last non NULL character
            while (mblen > 1  && !(mb[mblen-1]))
                mblen--;
            //check whether,  we hit an invalid character in the middle
            if ((mblen <= 1) || (remainingChars && state_data))
                return convertToUnicodeCharByChar(in, state);
            //Remove the last character and try again...
            state_data = mb[mblen-1];
            remainingChars = 1;
            mblen--;
        } else {
            // Fail.
            qWarning("MultiByteToWideChar: Cannot convert multibyte text");
            break;
        }
    }
 
    if (len <= 0)
        return QString();
 
    if (wc[len-1] == 0) // len - 1: we don't want terminator
        --len;
 
    //save the new state information
    if (state) {
        state->state_data[0] = (char)state_data;
        state->remainingChars = remainingChars;
    }
    QString s((QChar*)wc.data(), len);
    if (prepend) {
        return sp+s;
    }
    return s;
}
 
QByteArray QLocal8Bit::convertFromUnicode(QStringView in, QStringConverter::State *state)
{
    const QChar *ch = in.data();
    qsizetype uclen = in.size();
 
    Q_ASSERT(uclen < INT_MAX); // ### FIXME
    Q_ASSERT(state);
    Q_UNUSED(state); // ### Fixme
    if (state->flags & QStringConverter::Flag::Stateless) // temporary
        state = nullptr;
 
    if (!ch)
        return QByteArray();
    if (uclen == 0)
        return QByteArray("");
    BOOL used_def;
    QByteArray mb(4096, 0);
    int len;
    while (!(len=WideCharToMultiByte(CP_ACP, 0, (const wchar_t*)ch, uclen,
                mb.data(), mb.size()-1, 0, &used_def)))
    {
        int r = GetLastError();
        if (r == ERROR_INSUFFICIENT_BUFFER) {
            mb.resize(1+WideCharToMultiByte(CP_ACP, 0,
                                (const wchar_t*)ch, uclen,
                                0, 0, 0, &used_def));
                // and try again...
        } else {
            // Fail.  Probably can't happen in fact (dwFlags is 0).
#ifndef QT_NO_DEBUG
            // Can't use qWarning(), as it'll recurse to handle %ls
            fprintf(stderr,
                    "WideCharToMultiByte: Cannot convert multibyte text (error %d): %ls\n",
                    r, reinterpret_cast<const wchar_t*>(QString(ch, uclen).utf16()));
#endif
            break;
        }
    }
    mb.resize(len);
    return mb;
}
#endif
 
void QStringConverter::State::clear()
{
    if (clearFn)
        clearFn(this);
    else
        state_data[0] = state_data[1] = state_data[2] = state_data[3] = 0;
    remainingChars = 0;
    invalidChars = 0;
    internalState = 0;
}
 
static QChar *fromUtf16(QChar *out, QByteArrayView in, QStringConverter::State *state)
{
    return QUtf16::convertToUnicode(out, in, state, DetectEndianness);
}
 
static char *toUtf16(char *out, QStringView in, QStringConverter::State *state)
{
    return QUtf16::convertFromUnicode(out, in, state, DetectEndianness);
}
 
static QChar *fromUtf16BE(QChar *out, QByteArrayView in, QStringConverter::State *state)
{
    return QUtf16::convertToUnicode(out, in, state, BigEndianness);
}
 
static char *toUtf16BE(char *out, QStringView in, QStringConverter::State *state)
{
    return QUtf16::convertFromUnicode(out, in, state, BigEndianness);
}
 
static QChar *fromUtf16LE(QChar *out, QByteArrayView in, QStringConverter::State *state)
{
    return QUtf16::convertToUnicode(out, in, state, LittleEndianness);
}
 
static char *toUtf16LE(char *out, QStringView in, QStringConverter::State *state)
{
    return QUtf16::convertFromUnicode(out, in, state, LittleEndianness);
}
 
static QChar *fromUtf32(QChar *out, QByteArrayView in, QStringConverter::State *state)
{
    return QUtf32::convertToUnicode(out, in, state, DetectEndianness);
}
 
static char *toUtf32(char *out, QStringView in, QStringConverter::State *state)
{
    return QUtf32::convertFromUnicode(out, in, state, DetectEndianness);
}
 
static QChar *fromUtf32BE(QChar *out, QByteArrayView in, QStringConverter::State *state)
{
    return QUtf32::convertToUnicode(out, in, state, BigEndianness);
}
 
static char *toUtf32BE(char *out, QStringView in, QStringConverter::State *state)
{
    return QUtf32::convertFromUnicode(out, in, state, BigEndianness);
}
 
static QChar *fromUtf32LE(QChar *out, QByteArrayView in, QStringConverter::State *state)
{
    return QUtf32::convertToUnicode(out, in, state, LittleEndianness);
}
 
static char *toUtf32LE(char *out, QStringView in, QStringConverter::State *state)
{
    return QUtf32::convertFromUnicode(out, in, state, LittleEndianness);
}
 
void qt_from_latin1(char16_t *dst, const char *str, size_t size) noexcept;
 
static QChar *fromLatin1(QChar *out, QByteArrayView in, QStringConverter::State *state)
{
    Q_ASSERT(state);
    Q_UNUSED(state);
 
    qt_from_latin1(reinterpret_cast<char16_t *>(out), in.data(), size_t(in.size()));
    return out + in.size();
}
 
 
static char *toLatin1(char *out, QStringView in, QStringConverter::State *state)
{
    Q_ASSERT(state);
    if (state->flags & QStringConverter::Flag::Stateless) // temporary
        state = nullptr;
 
    const char replacement = (state && state->flags & QStringConverter::Flag::ConvertInvalidToNull) ? 0 : '?';
    qsizetype invalid = 0;
    for (qsizetype i = 0; i < in.length(); ++i) {
        if (in[i] > QChar(0xff)) {
            *out = replacement;
            ++invalid;
        } else {
            *out = (char)in[i].cell();
        }
        ++out;
    }
    if (state)
        state->invalidChars += invalid;
    return out;
}
 
static QChar *fromLocal8Bit(QChar *out, QByteArrayView in, QStringConverter::State *state)
{
    QString s = QLocal8Bit::convertToUnicode(in, state);
    memcpy(out, s.constData(), s.length()*sizeof(QChar));
    return out + s.length();
}
 
static char *toLocal8Bit(char *out, QStringView in, QStringConverter::State *state)
{
    QByteArray s = QLocal8Bit::convertFromUnicode(in, state);
    memcpy(out, s.constData(), s.length());
    return out + s.length();
}
 
 
static qsizetype fromUtf8Len(qsizetype l) { return l + 1; }
static qsizetype toUtf8Len(qsizetype l) { return 3*(l + 1); }
 
static qsizetype fromUtf16Len(qsizetype l) { return l/2 + 2; }
static qsizetype toUtf16Len(qsizetype l) { return 2*(l + 1); }
 
static qsizetype fromUtf32Len(qsizetype l) { return l/2 + 2; }
static qsizetype toUtf32Len(qsizetype l) { return 4*(l + 1); }
 
static qsizetype fromLatin1Len(qsizetype l) { return l + 1; }
static qsizetype toLatin1Len(qsizetype l) { return l + 1; }
 
 
 
const QStringConverter::Interface QStringConverter::encodingInterfaces[QStringConverter::LastEncoding + 1] =
{
    { "UTF-8", QUtf8::convertToUnicode, fromUtf8Len, QUtf8::convertFromUnicode, toUtf8Len },
    { "UTF-16", fromUtf16, fromUtf16Len, toUtf16, toUtf16Len },
    { "UTF-16LE", fromUtf16LE, fromUtf16Len, toUtf16LE, toUtf16Len },
    { "UTF-16BE", fromUtf16BE, fromUtf16Len, toUtf16BE, toUtf16Len },
    { "UTF-32", fromUtf32, fromUtf32Len, toUtf32, toUtf32Len },
    { "UTF-32LE", fromUtf32LE, fromUtf32Len, toUtf32LE, toUtf32Len },
    { "UTF-32BE", fromUtf32BE, fromUtf32Len, toUtf32BE, toUtf32Len },
    { "ISO-8859-1", fromLatin1, fromLatin1Len, toLatin1, toLatin1Len },
    { "Locale", fromLocal8Bit, fromUtf8Len, toLocal8Bit, toUtf8Len }
};
 
// match names case insensitive and skipping '-' and '_'
static bool nameMatch(const char *a, const char *b)
{
    while (*a && *b) {
        if (*a == '-' || *a == '_') {
            ++a;
            continue;
        }
        if (*b == '-' || *b == '_') {
            ++b;
            continue;
        }
        if (QtMiscUtils::toAsciiLower(*a) != QtMiscUtils::toAsciiLower(*b))
            return false;
        ++a;
        ++b;
    }
    return !*a && !*b;
}
 
 
QStringConverter::QStringConverter(const char *name, Flags f)
    : iface(nullptr), state(f)
{
    auto e = encodingForName(name);
    if (e)
        iface = encodingInterfaces + int(e.value());
}
 
std::optional<QStringConverter::Encoding> QStringConverter::encodingForName(const char *name)
{
    for (int i = 0; i < LastEncoding + 1; ++i) {
        if (nameMatch(encodingInterfaces[i].name, name))
            return QStringConverter::Encoding(i);
    }
    if (nameMatch(name, "latin1"))
        return QStringConverter::Latin1;
    return std::nullopt;
}
 
std::optional<QStringConverter::Encoding> QStringConverter::encodingForData(QByteArrayView data, char16_t expectedFirstCharacter)
{
    // someone set us up the BOM?
    qsizetype arraySize = data.size();
    if (arraySize > 3) {
        char32_t uc = qFromUnaligned<char32_t>(data.data());
        if (uc == qToBigEndian(char32_t(QChar::ByteOrderMark)))
            return QStringConverter::Utf32BE;
        if (uc == qToLittleEndian(char32_t(QChar::ByteOrderMark)))
            return QStringConverter::Utf32LE;
        if (expectedFirstCharacter) {
            // catch also anything starting with the expected character
            if (qToLittleEndian(uc) == expectedFirstCharacter)
                return QStringConverter::Utf32LE;
            else if (qToBigEndian(uc) == expectedFirstCharacter)
                return QStringConverter::Utf32BE;
        }
    }
 
    if (arraySize > 2) {
        if (memcmp(data.data(), utf8bom, sizeof(utf8bom)) == 0)
            return QStringConverter::Utf8;
    }
 
    if (arraySize > 1) {
        char16_t uc = qFromUnaligned<char16_t>(data.data());
        if (uc == qToBigEndian(char16_t(QChar::ByteOrderMark)))
            return QStringConverter::Utf16BE;
        if (uc == qToLittleEndian(char16_t(QChar::ByteOrderMark)))
            return QStringConverter::Utf16LE;
        if (expectedFirstCharacter) {
            // catch also anything starting with the expected character
            if (qToLittleEndian(uc) == expectedFirstCharacter)
                return QStringConverter::Utf16LE;
            else if (qToBigEndian(uc) == expectedFirstCharacter)
                return QStringConverter::Utf16BE;
        }
    }
    return std::nullopt;
}
 
std::optional<QStringConverter::Encoding> QStringConverter::encodingForHtml(QByteArrayView data)
{
    // determine charset
    auto encoding = encodingForData(data);
    if (encoding)
        // trust the initial BOM
        return encoding;
 
    static constexpr auto metaSearcher = qMakeStaticByteArrayMatcher("meta ");
    static constexpr auto charsetSearcher = qMakeStaticByteArrayMatcher("charset=");
 
    QByteArray header = data.first(qMin(data.size(), qsizetype(1024))).toByteArray().toLower();
    qsizetype pos = metaSearcher.indexIn(header);
    if (pos != -1) {
        pos = charsetSearcher.indexIn(header, pos);
        if (pos != -1) {
            pos += int(qstrlen("charset="));
            if (pos < header.size() && (header.at(pos) == '\"' || header.at(pos) == '\''))
                ++pos;
 
            qsizetype pos2 = pos;
            // The attribute can be closed with either """, "'", ">" or "/",
            // none of which are valid charset characters.
            while (++pos2 < header.size()) {
                char ch = header.at(pos2);
                if (ch == '\"' || ch == '\'' || ch == '>' || ch == '/') {
                    QByteArray name = header.mid(pos, pos2 - pos);
                    qsizetype colon = name.indexOf(':');
                    if (colon > 0)
                        name = name.left(colon);
                    name = name.simplified();
                    if (name == "unicode") // QTBUG-41998, ICU will return UTF-16.
                        name = QByteArrayLiteral("UTF-8");
                    if (!name.isEmpty())
                        return encodingForName(name);
                }
            }
        }
    }
    return Utf8;
}
 
const char *QStringConverter::nameForEncoding(QStringConverter::Encoding e)
{
    return encodingInterfaces[int(e)].name;
}
 
QT_END_NAMESPACE