/* Returns:
   - pointer to the last unprocessed character (a scalar fallback should check
   the rest);
   - nullptr if an error was detected.
*/
const char32_t *sse_validate_utf32le(const char32_t *input, size_t size) {
  const char32_t *end = input + size;

  const __m128i standardmax = _mm_set1_epi32(0x10ffff);
  const __m128i offset = _mm_set1_epi32(0xffff2000);
  const __m128i standardoffsetmax = _mm_set1_epi32(0xfffff7ff);
  __m128i currentmax = _mm_setzero_si128();
  __m128i currentoffsetmax = _mm_setzero_si128();

  while (input + 4 < end) {
    const __m128i in = _mm_loadu_si128((__m128i *)input);
    currentmax = _mm_max_epu32(in, currentmax);
    currentoffsetmax =
        _mm_max_epu32(_mm_add_epi32(in, offset), currentoffsetmax);
    input += 4;
  }
  __m128i is_zero =
      _mm_xor_si128(_mm_max_epu32(currentmax, standardmax), standardmax);
  if (_mm_test_all_zeros(is_zero, is_zero) == 0) {
    return nullptr;
  }

  is_zero = _mm_xor_si128(_mm_max_epu32(currentoffsetmax, standardoffsetmax),
                          standardoffsetmax);
  if (_mm_test_all_zeros(is_zero, is_zero) == 0) {
    return nullptr;
  }

  return input;
}

const result sse_validate_utf32le_with_errors(const char32_t *input,
                                              size_t size) {
  const char32_t *start = input;
  const char32_t *end = input + size;

  const __m128i standardmax = _mm_set1_epi32(0x10ffff);
  const __m128i offset = _mm_set1_epi32(0xffff2000);
  const __m128i standardoffsetmax = _mm_set1_epi32(0xfffff7ff);
  __m128i currentmax = _mm_setzero_si128();
  __m128i currentoffsetmax = _mm_setzero_si128();

  while (input + 4 < end) {
    const __m128i in = _mm_loadu_si128((__m128i *)input);
    currentmax = _mm_max_epu32(in, currentmax);
    currentoffsetmax =
        _mm_max_epu32(_mm_add_epi32(in, offset), currentoffsetmax);

    __m128i is_zero =
        _mm_xor_si128(_mm_max_epu32(currentmax, standardmax), standardmax);
    if (_mm_test_all_zeros(is_zero, is_zero) == 0) {
      return result(error_code::TOO_LARGE, input - start);
    }

    is_zero = _mm_xor_si128(_mm_max_epu32(currentoffsetmax, standardoffsetmax),
                            standardoffsetmax);
    if (_mm_test_all_zeros(is_zero, is_zero) == 0) {
      return result(error_code::SURROGATE, input - start);
    }
    input += 4;
  }

  return result(error_code::SUCCESS, input - start);
}