Function ExtractBitsSoftware

cpp/src/parquet/level_conversion_inc.h:237–260

};

inline uint64_t ExtractBitsSoftware(uint64_t bitmap, uint64_t select_bitmap) {
  // A software emulation of _pext_u64

  // These checks should be inline and are likely to be common cases.
  if (select_bitmap == ~uint64_t{0}) {
    return bitmap;
  } else if (select_bitmap == 0) {
    return 0;
  }

  // Fallback to lookup table method
  uint64_t bit_value = 0;
  int bit_len = 0;
  constexpr uint8_t kLookupMask = (1U << kLookupBits) - 1;
  while (select_bitmap != 0) {
    const auto mask_len = std::popcount(select_bitmap & kLookupMask);
    const uint64_t value = kPextTable[select_bitmap & kLookupMask][bitmap & kLookupMask];
    bit_value |= (value << bit_len);
    bit_len += mask_len;
    bitmap >>= kLookupBits;
    select_bitmap >>= kLookupBits;
  }
  return bit_value;
}

#ifdef ARROW_HAVE_BMI2