Function BM_Unpack

cpp/src/arrow/util/bpacking_benchmark.cc:73–104

template <typename Int>
void BM_Unpack(benchmark::State& state, bool aligned, UnpackFunc<Int> unpack, bool skip,
               std::string skip_msg) {
  if (skip) {
    state.SkipWithMessage(skip_msg);
  }

  const auto bit_width = static_cast<int32_t>(state.range(0));
  const auto num_values = static_cast<int32_t>(state.range(1));

  // Assume std::vector allocation is likely be aligned for greater than a byte.
  // So we allocate more values than necessary and skip to the next byte with the
  // desired (non) alignment to test the proper condition.
  constexpr int32_t kExtraValues = sizeof(Int) * 8;
  const auto packed = GenerateRandomPackedValues(num_values + kExtraValues, bit_width);
  const uint8_t* packed_ptr =
      GetNextAlignedByte(packed.data(), sizeof(Int)) + (aligned ? 0 : 1);

  auto unpacked = std::make_unique<Int[]>(num_values);

  const ::arrow::internal::UnpackOptions opts{
      .batch_size = num_values,
      .bit_width = bit_width,
      .bit_offset = 0,
      .max_read_bytes = -1,
  };

  for (auto _ : state) {
    unpack(packed_ptr, unpacked.get(), opts);
    benchmark::ClobberMemory();
  }
  state.SetItemsProcessed(num_values * state.iterations());
}

// Currently, the minimum unpack SIMD kernel size is 32 and the RLE-bit-packing encoder
// will not emit runs larger than 512 (though other implementation might), so we biased