Finding quote pairs with PCLMULQDQ

quotes-fragment.cpp

really_inline uint64_t find_quote_mask_and_bits(
    __m256i input_lo, __m256i input_hi, uint64_t odd_ends,
    uint64_t &prev_iter_inside_quote, uint64_t &quote_bits) {
  quote_bits =
      cmp_mask_against_input(input_lo, input_hi, _mm256_set1_epi8('"'));
  quote_bits = quote_bits & ~odd_ends;
  uint64_t quote_mask = _mm_cvtsi128_si64(_mm_clmulepi64_si128(
      _mm_set_epi64x(0ULL, quote_bits), _mm_set1_epi8(0xFF), 0));
  quote_mask ^= prev_iter_inside_quote;
  // right shift of a signed value expected to be well-defined and standard
  // compliant as of C++20,
  // John Regher from Utah U. says this is fine code
  prev_iter_inside_quote =
      static_cast<uint64_t>(static_cast<int64_t>(quote_mask) >> 63);
  return quote_mask;
}