inline bool Writer::ScanWriteUnescapedString()

in rapidjson/writer.h [538:596]
51 lines of code
11 McCabe index (conditional complexity)

inline bool Writer<StringBuffer>::ScanWriteUnescapedString(StringStream& is, size_t length) {
    if (length < 16)
        return RAPIDJSON_LIKELY(is.Tell() < length);

    if (!RAPIDJSON_LIKELY(is.Tell() < length))
        return false;

    const char* p = is.src_;
    const char* end = is.head_ + length;
    const char* nextAligned = reinterpret_cast<const char*>((reinterpret_cast<size_t>(p) + 15) & static_cast<size_t>(~15));
    const char* endAligned = reinterpret_cast<const char*>(reinterpret_cast<size_t>(end) & static_cast<size_t>(~15));
    if (nextAligned > end)
        return true;

    while (p != nextAligned)
        if (*p < 0x20 || *p == '\"' || *p == '\\') {
            is.src_ = p;
            return RAPIDJSON_LIKELY(is.Tell() < length);
        }
        else
            os_->PutUnsafe(*p++);

    // The rest of string using SIMD
    static const char dquote[16] = { '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"' };
    static const char bslash[16] = { '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\' };
    static const char space[16]  = { 0x19, 0x19, 0x19, 0x19, 0x19, 0x19, 0x19, 0x19, 0x19, 0x19, 0x19, 0x19, 0x19, 0x19, 0x19, 0x19 };
    const __m128i dq = _mm_loadu_si128(reinterpret_cast<const __m128i *>(&dquote[0]));
    const __m128i bs = _mm_loadu_si128(reinterpret_cast<const __m128i *>(&bslash[0]));
    const __m128i sp = _mm_loadu_si128(reinterpret_cast<const __m128i *>(&space[0]));

    for (; p != endAligned; p += 16) {
        const __m128i s = _mm_load_si128(reinterpret_cast<const __m128i *>(p));
        const __m128i t1 = _mm_cmpeq_epi8(s, dq);
        const __m128i t2 = _mm_cmpeq_epi8(s, bs);
        const __m128i t3 = _mm_cmpeq_epi8(_mm_max_epu8(s, sp), sp); // s < 0x20 <=> max(s, 0x19) == 0x19
        const __m128i x = _mm_or_si128(_mm_or_si128(t1, t2), t3);
        unsigned short r = static_cast<unsigned short>(_mm_movemask_epi8(x));
        if (RAPIDJSON_UNLIKELY(r != 0)) {   // some of characters is escaped
            SizeType len;
#ifdef _MSC_VER         // Find the index of first escaped
            unsigned long offset;
            _BitScanForward(&offset, r);
            len = offset;
#else
            len = static_cast<SizeType>(__builtin_ffs(r) - 1);
#endif
            char* q = reinterpret_cast<char*>(os_->PushUnsafe(len));
            for (size_t i = 0; i < len; i++)
                q[i] = p[i];

            p += len;
            break;
        }
        _mm_storeu_si128(reinterpret_cast<__m128i *>(os_->PushUnsafe(16)), s);
    }

    is.src_ = p;
    return RAPIDJSON_LIKELY(is.Tell() < length);
}