std::pair<const char *, char32_t *>
sse_convert_latin1_to_utf32(const char *buf, size_t len,
                            char32_t *utf32_output) {
  const char *end = buf + len;

  while (end - buf >= 16) {
    // Load 16 Latin1 characters (16 bytes) into a 128-bit register
    __m128i in = _mm_loadu_si128((__m128i *)buf);

    // Shift input to process next 4 bytes
    __m128i in_shifted1 = _mm_srli_si128(in, 4);
    __m128i in_shifted2 = _mm_srli_si128(in, 8);
    __m128i in_shifted3 = _mm_srli_si128(in, 12);

    // expand 8-bit to 32-bit unit
    __m128i out1 = _mm_cvtepu8_epi32(in);
    __m128i out2 = _mm_cvtepu8_epi32(in_shifted1);
    __m128i out3 = _mm_cvtepu8_epi32(in_shifted2);
    __m128i out4 = _mm_cvtepu8_epi32(in_shifted3);

    _mm_storeu_si128((__m128i *)utf32_output, out1);
    _mm_storeu_si128((__m128i *)(utf32_output + 4), out2);
    _mm_storeu_si128((__m128i *)(utf32_output + 8), out3);
    _mm_storeu_si128((__m128i *)(utf32_output + 12), out4);

    utf32_output += 16;
    buf += 16;
  }

  return std::make_pair(buf, utf32_output);
}