static RAPIDJSON_FORCEINLINE void ScanCopyUnescapedString()

in rapidjson/reader.h [965:1021]
49 lines of code
9 McCabe index (conditional complexity)

    static RAPIDJSON_FORCEINLINE void ScanCopyUnescapedString(InsituStringStream& is, InsituStringStream& os) {
        RAPIDJSON_ASSERT(&is == &os);
        (void)os;

        if (is.src_ == is.dst_) {
            SkipUnescapedString(is);
            return;
        }

        char* p = is.src_;
        char *q = is.dst_;

        // Scan one by one until alignment (unaligned load may cross page boundary and cause crash)
        const char* nextAligned = reinterpret_cast<const char*>((reinterpret_cast<size_t>(p) + 15) & static_cast<size_t>(~15));
        while (p != nextAligned)
            if (RAPIDJSON_UNLIKELY(*p == '\"') || RAPIDJSON_UNLIKELY(*p == '\\') || RAPIDJSON_UNLIKELY(static_cast<unsigned>(*p) < 0x20)) {
                is.src_ = p;
                is.dst_ = q;
                return;
            }
            else
                *q++ = *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 += 16, q += 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
                size_t length;
#ifdef _MSC_VER         // Find the index of first escaped
                unsigned long offset;
                _BitScanForward(&offset, r);
                length = offset;
#else
                length = static_cast<size_t>(__builtin_ffs(r) - 1);
#endif
                for (const char* pend = p + length; p != pend; )
                    *q++ = *p++;
                break;
            }
            _mm_storeu_si128(reinterpret_cast<__m128i *>(q), s);
        }

        is.src_ = p;
        is.dst_ = q;
    }