#include "arrow/compute/row/encode_internal.h"

namespace arrow {
namespace compute {

void RowTableEncoder::Init(const std::vector<KeyColumnMetadata>& cols, LightContext* ctx,
                           int row_alignment, int string_alignment) {
  ctx_ = ctx;
  row_metadata_.FromColumnMetadataVector(cols, row_alignment, string_alignment);
  uint32_t num_cols = row_metadata_.num_cols();
  uint32_t num_varbinary_cols = row_metadata_.num_varbinary_cols();
  batch_all_cols_.resize(num_cols);
  batch_varbinary_cols_.resize(num_varbinary_cols);
  batch_varbinary_cols_base_offsets_.resize(num_varbinary_cols);
}

void RowTableEncoder::PrepareKeyColumnArrays(int64_t start_row, int64_t num_rows,
                                             const std::vector<KeyColumnArray>& cols_in) {
  const auto num_cols = static_cast<uint32_t>(cols_in.size());
  DCHECK(batch_all_cols_.size() == num_cols);

  uint32_t num_varbinary_visited = 0;
  for (uint32_t i = 0; i < num_cols; ++i) {
    const KeyColumnArray& col = cols_in[row_metadata_.column_order[i]];
    KeyColumnArray col_window = col.Slice(start_row, num_rows);

    batch_all_cols_[i] = col_window;
    if (!col.metadata().is_fixed_length) {
      DCHECK(num_varbinary_visited < batch_varbinary_cols_.size());

      if (start_row == 0) {
        batch_varbinary_cols_base_offsets_[num_varbinary_visited] = 0;
      } else {
        batch_varbinary_cols_base_offsets_[num_varbinary_visited] =
            col.offsets()[start_row];
      }
      batch_varbinary_cols_[num_varbinary_visited++] = col_window;
    }
  }
}

void RowTableEncoder::DecodeFixedLengthBuffers(int64_t start_row_input,
                                               int64_t start_row_output, int64_t num_rows,
                                               const RowTableImpl& rows,
                                               std::vector<KeyColumnArray>* cols) {

  PrepareKeyColumnArrays(start_row_output, num_rows, *cols);

  auto temp_buffer_holder_A =
      util::TempVectorHolder<uint16_t>(ctx_->stack, static_cast<uint32_t>(num_rows));
  auto temp_buffer_A = KeyColumnArray(
      KeyColumnMetadata(true, sizeof(uint16_t)), num_rows, nullptr,
      reinterpret_cast<uint8_t*>(temp_buffer_holder_A.mutable_data()), nullptr);
  auto temp_buffer_holder_B =
      util::TempVectorHolder<uint16_t>(ctx_->stack, static_cast<uint32_t>(num_rows));
  auto temp_buffer_B = KeyColumnArray(
      KeyColumnMetadata(true, sizeof(uint16_t)), num_rows, nullptr,
      reinterpret_cast<uint8_t*>(temp_buffer_holder_B.mutable_data()), nullptr);

  bool is_row_fixed_length = row_metadata_.is_fixed_length;
  if (!is_row_fixed_length) {
    EncoderOffsets::Decode(static_cast<uint32_t>(start_row_input),
                           static_cast<uint32_t>(num_rows), rows, &batch_varbinary_cols_,
                           batch_varbinary_cols_base_offsets_, ctx_);
  }

  const auto num_cols = static_cast<uint32_t>(batch_all_cols_.size());
  for (uint32_t i = 0; i < num_cols;) {
    if (!batch_all_cols_[i].metadata().is_fixed_length ||
        batch_all_cols_[i].metadata().is_null_type) {
      i += 1;
      continue;
    }
    bool can_process_pair =
        (i + 1 < num_cols) && batch_all_cols_[i + 1].metadata().is_fixed_length &&
        EncoderBinaryPair::CanProcessPair(batch_all_cols_[i].metadata(),
                                          batch_all_cols_[i + 1].metadata());
    if (!can_process_pair) {
      EncoderBinary::Decode(static_cast<uint32_t>(start_row_input),
                            static_cast<uint32_t>(num_rows),
                            row_metadata_.column_offsets[i], rows, &batch_all_cols_[i],
                            ctx_, &temp_buffer_A);
      i += 1;
    } else {
      EncoderBinaryPair::Decode(
          static_cast<uint32_t>(start_row_input), static_cast<uint32_t>(num_rows),
          row_metadata_.column_offsets[i], rows, &batch_all_cols_[i],
          &batch_all_cols_[i + 1], ctx_, &temp_buffer_A, &temp_buffer_B);
      i += 2;
    }
  }

  EncoderNulls::Decode(static_cast<uint32_t>(start_row_input),
                       static_cast<uint32_t>(num_rows), rows, &batch_all_cols_);
}

void RowTableEncoder::DecodeVaryingLengthBuffers(int64_t start_row_input,
                                                 int64_t start_row_output,
                                                 int64_t num_rows,
                                                 const RowTableImpl& rows,
                                                 std::vector<KeyColumnArray>* cols) {

  PrepareKeyColumnArrays(start_row_output, num_rows, *cols);

  bool is_row_fixed_length = row_metadata_.is_fixed_length;
  if (!is_row_fixed_length) {
    for (size_t i = 0; i < batch_varbinary_cols_.size(); ++i) {

      EncoderVarBinary::Decode(static_cast<uint32_t>(start_row_input),
                               static_cast<uint32_t>(num_rows), static_cast<uint32_t>(i),
                               rows, &batch_varbinary_cols_[i], ctx_);
    }
  }
}

void RowTableEncoder::PrepareEncodeSelected(int64_t start_row, int64_t num_rows,
                                            const std::vector<KeyColumnArray>& cols) {

  PrepareKeyColumnArrays(start_row, num_rows, cols);
}

Status RowTableEncoder::EncodeSelected(RowTableImpl* rows, uint32_t num_selected,
                                       const uint16_t* selection) {
  rows->Clean();
  RETURN_NOT_OK(
      rows->AppendEmpty(static_cast<uint32_t>(num_selected), static_cast<uint32_t>(0)));

  EncoderOffsets::GetRowOffsetsSelected(rows, batch_varbinary_cols_, num_selected,
                                        selection);

  RETURN_NOT_OK(rows->AppendEmpty(static_cast<uint32_t>(0),
                                  static_cast<uint32_t>(rows->offsets()[num_selected])));

  for (size_t icol = 0; icol < batch_all_cols_.size(); ++icol) {
    if (batch_all_cols_[icol].metadata().is_fixed_length) {
      uint32_t offset_within_row = rows->metadata().column_offsets[icol];
      EncoderBinary::EncodeSelected(offset_within_row, rows, batch_all_cols_[icol],
                                    num_selected, selection);
    }
  }

  EncoderOffsets::EncodeSelected(rows, batch_varbinary_cols_, num_selected, selection);

  for (size_t icol = 0; icol < batch_varbinary_cols_.size(); ++icol) {
    EncoderVarBinary::EncodeSelected(static_cast<uint32_t>(icol), rows,
                                     batch_varbinary_cols_[icol], num_selected,
                                     selection);
  }

  EncoderNulls::EncodeSelected(rows, batch_all_cols_, num_selected, selection);

  return Status::OK();
}

namespace {
struct TransformBoolean {
  static KeyColumnArray ArrayReplace(const KeyColumnArray& column,
                                     const KeyColumnArray& temp) {

    DCHECK(temp.length() >= column.length() && temp.metadata().is_fixed_length &&
           temp.metadata().fixed_length >= sizeof(uint8_t));
    KeyColumnMetadata metadata;
    metadata.is_fixed_length = true;
    metadata.fixed_length = sizeof(uint8_t);
    constexpr int buffer_index = 1;
    return column.WithBufferFrom(temp, buffer_index).WithMetadata(metadata);
  }

  static void PostDecode(const KeyColumnArray& input, KeyColumnArray* output,
                         LightContext* ctx) {

    DCHECK(output->metadata().is_fixed_length == input.metadata().is_fixed_length);
    DCHECK(output->metadata().fixed_length == 0 && input.metadata().fixed_length == 1);
    DCHECK(output->length() == input.length());
    constexpr int buffer_index = 1;
    DCHECK(input.data(buffer_index) != nullptr);
    DCHECK(output->mutable_data(buffer_index) != nullptr);

    util::bit_util::bytes_to_bits(
        ctx->hardware_flags, static_cast<int>(input.length()), input.data(buffer_index),
        output->mutable_data(buffer_index), output->bit_offset(buffer_index));
  }
};

}  

bool EncoderInteger::IsBoolean(const KeyColumnMetadata& metadata) {
  return metadata.is_fixed_length && metadata.fixed_length == 0 && !metadata.is_null_type;
}

bool EncoderInteger::UsesTransform(const KeyColumnArray& column) {
  return IsBoolean(column.metadata());
}

KeyColumnArray EncoderInteger::ArrayReplace(const KeyColumnArray& column,
                                            const KeyColumnArray& temp) {
  if (IsBoolean(column.metadata())) {
    return TransformBoolean::ArrayReplace(column, temp);
  }
  return column;
}

void EncoderInteger::PostDecode(const KeyColumnArray& input, KeyColumnArray* output,
                                LightContext* ctx) {
  if (IsBoolean(output->metadata())) {
    TransformBoolean::PostDecode(input, output, ctx);
  }
}

void EncoderInteger::Decode(uint32_t start_row, uint32_t num_rows,
                            uint32_t offset_within_row, const RowTableImpl& rows,
                            KeyColumnArray* col, LightContext* ctx,
                            KeyColumnArray* temp) {
  KeyColumnArray col_prep;
  if (UsesTransform(*col)) {
    col_prep = ArrayReplace(*col, *temp);
  } else {
    col_prep = *col;
  }

  if (rows.metadata().is_fixed_length &&
      col_prep.metadata().fixed_length == rows.metadata().fixed_length) {
    DCHECK_EQ(offset_within_row, 0);
    uint32_t row_size = rows.metadata().fixed_length;
    memcpy(col_prep.mutable_data(1), rows.data(1) + start_row * row_size,
           num_rows * row_size);
  } else if (rows.metadata().is_fixed_length) {
    uint32_t row_size = rows.metadata().fixed_length;
    const uint8_t* row_base = rows.data(1) + start_row * row_size;
    row_base += offset_within_row;
    uint8_t* col_base = col_prep.mutable_data(1);
    switch (col_prep.metadata().fixed_length) {
      case 1:
        for (uint32_t i = 0; i < num_rows; ++i) {
          col_base[i] = row_base[i * row_size];
        }
        break;
      case 2:
        for (uint32_t i = 0; i < num_rows; ++i) {
          reinterpret_cast<uint16_t*>(col_base)[i] =
              *reinterpret_cast<const uint16_t*>(row_base + i * row_size);
        }
        break;
      case 4:
        for (uint32_t i = 0; i < num_rows; ++i) {
          reinterpret_cast<uint32_t*>(col_base)[i] =
              *reinterpret_cast<const uint32_t*>(row_base + i * row_size);
        }
        break;
      case 8:
        for (uint32_t i = 0; i < num_rows; ++i) {
          reinterpret_cast<uint64_t*>(col_base)[i] =
              *reinterpret_cast<const uint64_t*>(row_base + i * row_size);
        }
        break;
      default:
        DCHECK(false);
    }
  } else {
    const uint32_t* row_offsets = rows.offsets() + start_row;
    const uint8_t* row_base = rows.data(2);
    row_base += offset_within_row;
    uint8_t* col_base = col_prep.mutable_data(1);
    switch (col_prep.metadata().fixed_length) {
      case 1:
        for (uint32_t i = 0; i < num_rows; ++i) {
          col_base[i] = row_base[row_offsets[i]];
        }
        break;
      case 2:
        for (uint32_t i = 0; i < num_rows; ++i) {
          reinterpret_cast<uint16_t*>(col_base)[i] =
              *reinterpret_cast<const uint16_t*>(row_base + row_offsets[i]);
        }
        break;
      case 4:
        for (uint32_t i = 0; i < num_rows; ++i) {
          reinterpret_cast<uint32_t*>(col_base)[i] =
              *reinterpret_cast<const uint32_t*>(row_base + row_offsets[i]);
        }
        break;
      case 8:
        for (uint32_t i = 0; i < num_rows; ++i) {
          reinterpret_cast<uint64_t*>(col_base)[i] =
              *reinterpret_cast<const uint64_t*>(row_base + row_offsets[i]);
        }
        break;
      default:
        DCHECK(false);
    }
  }

  if (UsesTransform(*col)) {
    PostDecode(col_prep, col, ctx);
  }
}

template <class COPY_FN, class SET_NULL_FN>
void EncoderBinary::EncodeSelectedImp(uint32_t offset_within_row, RowTableImpl* rows,
                                      const KeyColumnArray& col, uint32_t num_selected,
                                      const uint16_t* selection, COPY_FN copy_fn,
                                      SET_NULL_FN set_null_fn) {
  bool is_fixed_length = rows->metadata().is_fixed_length;
  if (is_fixed_length) {
    uint32_t row_width = rows->metadata().fixed_length;
    const uint8_t* src_base = col.data(1);
    uint8_t* dst = rows->mutable_data(1) + offset_within_row;
    for (uint32_t i = 0; i < num_selected; ++i) {
      copy_fn(dst, src_base, selection[i]);
      dst += row_width;
    }
    if (col.data(0)) {
      const uint8_t* non_null_bits = col.data(0);
      uint8_t* dst = rows->mutable_data(1) + offset_within_row;
      for (uint32_t i = 0; i < num_selected; ++i) {
        bool is_null = !bit_util::GetBit(non_null_bits, selection[i] + col.bit_offset(0));
        if (is_null) {
          set_null_fn(dst);
        }
        dst += row_width;
      }
    }
  } else {
    const uint8_t* src_base = col.data(1);
    uint8_t* dst = rows->mutable_data(2) + offset_within_row;
    const uint32_t* offsets = rows->offsets();
    for (uint32_t i = 0; i < num_selected; ++i) {
      copy_fn(dst + offsets[i], src_base, selection[i]);
    }
    if (col.data(0)) {
      const uint8_t* non_null_bits = col.data(0);
      uint8_t* dst = rows->mutable_data(2) + offset_within_row;
      const uint32_t* offsets = rows->offsets();
      for (uint32_t i = 0; i < num_selected; ++i) {
        bool is_null = !bit_util::GetBit(non_null_bits, selection[i] + col.bit_offset(0));
        if (is_null) {
          set_null_fn(dst + offsets[i]);
        }
      }
    }
  }
}

void EncoderBinary::EncodeSelected(uint32_t offset_within_row, RowTableImpl* rows,
                                   const KeyColumnArray& col, uint32_t num_selected,
                                   const uint16_t* selection) {
  if (col.metadata().is_null_type) {
    return;
  }
  uint32_t col_width = col.metadata().fixed_length;
  if (col_width == 0) {
    int bit_offset = col.bit_offset(1);
    EncodeSelectedImp(
        offset_within_row, rows, col, num_selected, selection,
        [bit_offset](uint8_t* dst, const uint8_t* src_base, uint16_t irow) {
          *dst = bit_util::GetBit(src_base, irow + bit_offset) ? 0xff : 0x00;
        },
        [](uint8_t* dst) { *dst = 0xae; });
  } else if (col_width == 1) {
    EncodeSelectedImp(
        offset_within_row, rows, col, num_selected, selection,
        [](uint8_t* dst, const uint8_t* src_base, uint16_t irow) {
          *dst = src_base[irow];
        },
        [](uint8_t* dst) { *dst = 0xae; });
  } else if (col_width == 2) {
    EncodeSelectedImp(
        offset_within_row, rows, col, num_selected, selection,
        [](uint8_t* dst, const uint8_t* src_base, uint16_t irow) {
          *reinterpret_cast<uint16_t*>(dst) =
              reinterpret_cast<const uint16_t*>(src_base)[irow];
        },
        [](uint8_t* dst) { *reinterpret_cast<uint16_t*>(dst) = 0xaeae; });
  } else if (col_width == 4) {
    EncodeSelectedImp(
        offset_within_row, rows, col, num_selected, selection,
        [](uint8_t* dst, const uint8_t* src_base, uint16_t irow) {
          *reinterpret_cast<uint32_t*>(dst) =
              reinterpret_cast<const uint32_t*>(src_base)[irow];
        },
        [](uint8_t* dst) {
          *reinterpret_cast<uint32_t*>(dst) = static_cast<uint32_t>(0xaeaeaeae);
        });
  } else if (col_width == 8) {
    EncodeSelectedImp(
        offset_within_row, rows, col, num_selected, selection,
        [](uint8_t* dst, const uint8_t* src_base, uint16_t irow) {
          *reinterpret_cast<uint64_t*>(dst) =
              reinterpret_cast<const uint64_t*>(src_base)[irow];
        },
        [](uint8_t* dst) { *reinterpret_cast<uint64_t*>(dst) = 0xaeaeaeaeaeaeaeaeULL; });
  } else {
    EncodeSelectedImp(
        offset_within_row, rows, col, num_selected, selection,
        [col_width](uint8_t* dst, const uint8_t* src_base, uint16_t irow) {
          memcpy(dst, src_base + col_width * irow, col_width);
        },
        [col_width](uint8_t* dst) { memset(dst, 0xae, col_width); });
  }
}

bool EncoderBinary::IsInteger(const KeyColumnMetadata& metadata) {
  if (metadata.is_null_type) {
    return false;
  }
  bool is_fixed_length = metadata.is_fixed_length;
  auto size = metadata.fixed_length;
  return is_fixed_length &&
         (size == 0 || size == 1 || size == 2 || size == 4 || size == 8);
}

void EncoderBinary::Decode(uint32_t start_row, uint32_t num_rows,
                           uint32_t offset_within_row, const RowTableImpl& rows,
                           KeyColumnArray* col, LightContext* ctx, KeyColumnArray* temp) {
  if (IsInteger(col->metadata())) {
    EncoderInteger::Decode(start_row, num_rows, offset_within_row, rows, col, ctx, temp);
  } else {
    KeyColumnArray col_prep;
    if (EncoderInteger::UsesTransform(*col)) {
      col_prep = EncoderInteger::ArrayReplace(*col, *temp);
    } else {
      col_prep = *col;
    }

    bool is_row_fixed_length = rows.metadata().is_fixed_length;

#if defined(ARROW_HAVE_AVX2)
    if (ctx->has_avx2()) {
      DecodeHelper_avx2(is_row_fixed_length, start_row, num_rows, offset_within_row, rows,
                        col);
    } else {
#endif
      if (is_row_fixed_length) {
        DecodeImp<true>(start_row, num_rows, offset_within_row, rows, col);
      } else {
        DecodeImp<false>(start_row, num_rows, offset_within_row, rows, col);
      }
#if defined(ARROW_HAVE_AVX2)
    }
#endif

    if (EncoderInteger::UsesTransform(*col)) {
      EncoderInteger::PostDecode(col_prep, col, ctx);
    }
  }
}

template <bool is_row_fixed_length>
void EncoderBinary::DecodeImp(uint32_t start_row, uint32_t num_rows,
                              uint32_t offset_within_row, const RowTableImpl& rows,
                              KeyColumnArray* col) {
  DecodeHelper<is_row_fixed_length>(
      start_row, num_rows, offset_within_row, &rows, nullptr, col, col,
      [](uint8_t* dst, const uint8_t* src, int64_t length) {
        for (uint32_t istripe = 0; istripe < bit_util::CeilDiv(length, 8); ++istripe) {
          auto dst64 = reinterpret_cast<uint64_t*>(dst);
          auto src64 = reinterpret_cast<const uint64_t*>(src);
          util::SafeStore(dst64 + istripe, src64[istripe]);
        }
      });
}

void EncoderBinaryPair::Decode(uint32_t start_row, uint32_t num_rows,
                               uint32_t offset_within_row, const RowTableImpl& rows,
                               KeyColumnArray* col1, KeyColumnArray* col2,
                               LightContext* ctx, KeyColumnArray* temp1,
                               KeyColumnArray* temp2) {
  DCHECK(CanProcessPair(col1->metadata(), col2->metadata()));

  KeyColumnArray col_prep[2];
  if (EncoderInteger::UsesTransform(*col1)) {
    col_prep[0] = EncoderInteger::ArrayReplace(*col1, *temp1);
  } else {
    col_prep[0] = *col1;
  }
  if (EncoderInteger::UsesTransform(*col2)) {
    col_prep[1] = EncoderInteger::ArrayReplace(*col2, *temp2);
  } else {
    col_prep[1] = *col2;
  }

  uint32_t col_width1 = col_prep[0].metadata().fixed_length;
  uint32_t col_width2 = col_prep[1].metadata().fixed_length;
  int log_col_width1 = col_width1 == 8   ? 3
                       : col_width1 == 4 ? 2
                       : col_width1 == 2 ? 1
                                         : 0;
  int log_col_width2 = col_width2 == 8   ? 3
                       : col_width2 == 4 ? 2
                       : col_width2 == 2 ? 1
                                         : 0;

  bool is_row_fixed_length = rows.metadata().is_fixed_length;

  uint32_t num_processed = 0;
#if defined(ARROW_HAVE_AVX2)
  if (ctx->has_avx2() && col_width1 == col_width2) {
    num_processed =
        DecodeHelper_avx2(is_row_fixed_length, col_width1, start_row, num_rows,
                          offset_within_row, rows, &col_prep[0], &col_prep[1]);
  }
#endif
  if (num_processed < num_rows) {
    using DecodeImp_t = void (*)(uint32_t, uint32_t, uint32_t, uint32_t,
                                 const RowTableImpl&, KeyColumnArray*, KeyColumnArray*);
    static const DecodeImp_t DecodeImp_fn[] = {
        DecodeImp<false, uint8_t, uint8_t>,   DecodeImp<false, uint16_t, uint8_t>,
        DecodeImp<false, uint32_t, uint8_t>,  DecodeImp<false, uint64_t, uint8_t>,
        DecodeImp<false, uint8_t, uint16_t>,  DecodeImp<false, uint16_t, uint16_t>,
        DecodeImp<false, uint32_t, uint16_t>, DecodeImp<false, uint64_t, uint16_t>,
        DecodeImp<false, uint8_t, uint32_t>,  DecodeImp<false, uint16_t, uint32_t>,
        DecodeImp<false, uint32_t, uint32_t>, DecodeImp<false, uint64_t, uint32_t>,
        DecodeImp<false, uint8_t, uint64_t>,  DecodeImp<false, uint16_t, uint64_t>,
        DecodeImp<false, uint32_t, uint64_t>, DecodeImp<false, uint64_t, uint64_t>,
        DecodeImp<true, uint8_t, uint8_t>,    DecodeImp<true, uint16_t, uint8_t>,
        DecodeImp<true, uint32_t, uint8_t>,   DecodeImp<true, uint64_t, uint8_t>,
        DecodeImp<true, uint8_t, uint16_t>,   DecodeImp<true, uint16_t, uint16_t>,
        DecodeImp<true, uint32_t, uint16_t>,  DecodeImp<true, uint64_t, uint16_t>,
        DecodeImp<true, uint8_t, uint32_t>,   DecodeImp<true, uint16_t, uint32_t>,
        DecodeImp<true, uint32_t, uint32_t>,  DecodeImp<true, uint64_t, uint32_t>,
        DecodeImp<true, uint8_t, uint64_t>,   DecodeImp<true, uint16_t, uint64_t>,
        DecodeImp<true, uint32_t, uint64_t>,  DecodeImp<true, uint64_t, uint64_t>};
    int dispatch_const =
        (log_col_width2 << 2) | log_col_width1 | (is_row_fixed_length ? 16 : 0);
    DecodeImp_fn[dispatch_const](num_processed, start_row, num_rows, offset_within_row,
                                 rows, &(col_prep[0]), &(col_prep[1]));
  }

  if (EncoderInteger::UsesTransform(*col1)) {
    EncoderInteger::PostDecode(col_prep[0], col1, ctx);
  }
  if (EncoderInteger::UsesTransform(*col2)) {
    EncoderInteger::PostDecode(col_prep[1], col2, ctx);
  }
}

template <bool is_row_fixed_length, typename col1_type, typename col2_type>
void EncoderBinaryPair::DecodeImp(uint32_t num_rows_to_skip, uint32_t start_row,
                                  uint32_t num_rows, uint32_t offset_within_row,
                                  const RowTableImpl& rows, KeyColumnArray* col1,
                                  KeyColumnArray* col2) {
  DCHECK(rows.length() >= start_row + num_rows);
  DCHECK(col1->length() == num_rows && col2->length() == num_rows);

  uint8_t* dst_A = col1->mutable_data(1);
  uint8_t* dst_B = col2->mutable_data(1);

  uint32_t fixed_length = rows.metadata().fixed_length;
  const uint32_t* offsets;
  const uint8_t* src_base;
  if (is_row_fixed_length) {
    src_base = rows.data(1) + fixed_length * start_row + offset_within_row;
    offsets = nullptr;
  } else {
    src_base = rows.data(2) + offset_within_row;
    offsets = rows.offsets() + start_row;
  }

  using col1_type_const = typename std::add_const<col1_type>::type;
  using col2_type_const = typename std::add_const<col2_type>::type;

  if (is_row_fixed_length) {
    const uint8_t* src = src_base + num_rows_to_skip * fixed_length;
    for (uint32_t i = num_rows_to_skip; i < num_rows; ++i) {
      reinterpret_cast<col1_type*>(dst_A)[i] = *reinterpret_cast<col1_type_const*>(src);
      reinterpret_cast<col2_type*>(dst_B)[i] =
          *reinterpret_cast<col2_type_const*>(src + sizeof(col1_type));
      src += fixed_length;
    }
  } else {
    for (uint32_t i = num_rows_to_skip; i < num_rows; ++i) {
      const uint8_t* src = src_base + offsets[i];
      reinterpret_cast<col1_type*>(dst_A)[i] = *reinterpret_cast<col1_type_const*>(src);
      reinterpret_cast<col2_type*>(dst_B)[i] =
          *reinterpret_cast<col2_type_const*>(src + sizeof(col1_type));
    }
  }
}

void EncoderOffsets::Decode(uint32_t start_row, uint32_t num_rows,
                            const RowTableImpl& rows,
                            std::vector<KeyColumnArray>* varbinary_cols,
                            const std::vector<uint32_t>& varbinary_cols_base_offset,
                            LightContext* ctx) {
  DCHECK(!varbinary_cols->empty());
  DCHECK(varbinary_cols->size() == varbinary_cols_base_offset.size());

  DCHECK(!rows.metadata().is_fixed_length);
  DCHECK(rows.length() >= start_row + num_rows);
  for (const auto& col : *varbinary_cols) {

    DCHECK(!col.metadata().is_fixed_length);

    DCHECK(col.length() == num_rows);
  }

  const uint32_t* row_offsets = rows.offsets() + start_row;

  for (size_t col = 0; col < varbinary_cols->size(); ++col) {
    uint32_t* col_offsets = (*varbinary_cols)[col].mutable_offsets();
    col_offsets[0] = varbinary_cols_base_offset[col];
  }

  int string_alignment = rows.metadata().string_alignment;

  for (uint32_t i = 0; i < num_rows; ++i) {

    const uint8_t* row = rows.data(2) + row_offsets[i];
    const uint32_t* varbinary_ends = rows.metadata().varbinary_end_array(row);

    uint32_t offset_within_row = rows.metadata().fixed_length;
    for (size_t col = 0; col < varbinary_cols->size(); ++col) {
      offset_within_row +=
          RowTableMetadata::padding_for_alignment(offset_within_row, string_alignment);
      uint32_t length = varbinary_ends[col] - offset_within_row;
      offset_within_row = varbinary_ends[col];
      uint32_t* col_offsets = (*varbinary_cols)[col].mutable_offsets();
      col_offsets[i + 1] = col_offsets[i] + length;
    }
  }
}

void EncoderOffsets::GetRowOffsetsSelected(RowTableImpl* rows,
                                           const std::vector<KeyColumnArray>& cols,
                                           uint32_t num_selected,
                                           const uint16_t* selection) {
  if (rows->metadata().is_fixed_length) {
    return;
  }

  uint32_t* row_offsets = rows->mutable_offsets();
  for (uint32_t i = 0; i < num_selected; ++i) {
    row_offsets[i] = rows->metadata().fixed_length;
  }

  for (size_t icol = 0; icol < cols.size(); ++icol) {
    bool is_fixed_length = (cols[icol].metadata().is_fixed_length);
    if (!is_fixed_length) {
      const uint32_t* col_offsets = cols[icol].offsets();
      for (uint32_t i = 0; i < num_selected; ++i) {
        uint32_t irow = selection[i];
        uint32_t length = col_offsets[irow + 1] - col_offsets[irow];
        row_offsets[i] += RowTableMetadata::padding_for_alignment(
            row_offsets[i], rows->metadata().string_alignment);
        row_offsets[i] += length;
      }
      const uint8_t* non_null_bits = cols[icol].data(0);
      if (non_null_bits) {
        const uint32_t* col_offsets = cols[icol].offsets();
        for (uint32_t i = 0; i < num_selected; ++i) {
          uint32_t irow = selection[i];
          bool is_null =
              !bit_util::GetBit(non_null_bits, irow + cols[icol].bit_offset(0));
          if (is_null) {
            uint32_t length = col_offsets[irow + 1] - col_offsets[irow];
            row_offsets[i] -= length;
          }
        }
      }
    }
  }

  uint32_t sum = 0;
  int row_alignment = rows->metadata().row_alignment;
  for (uint32_t i = 0; i < num_selected; ++i) {
    uint32_t length = row_offsets[i];
    length += RowTableMetadata::padding_for_alignment(length, row_alignment);
    row_offsets[i] = sum;
    sum += length;
  }
  row_offsets[num_selected] = sum;
}

template <bool has_nulls, bool is_first_varbinary>
void EncoderOffsets::EncodeSelectedImp(uint32_t ivarbinary, RowTableImpl* rows,
                                       const std::vector<KeyColumnArray>& cols,
                                       uint32_t num_selected, const uint16_t* selection) {
  const uint32_t* row_offsets = rows->offsets();
  uint8_t* row_base = rows->mutable_data(2) +
                      rows->metadata().varbinary_end_array_offset +
                      ivarbinary * sizeof(uint32_t);
  const uint32_t* col_offsets = cols[ivarbinary].offsets();
  const uint8_t* col_non_null_bits = cols[ivarbinary].data(0);

  for (uint32_t i = 0; i < num_selected; ++i) {
    uint32_t irow = selection[i];
    uint32_t length = col_offsets[irow + 1] - col_offsets[irow];
    if (has_nulls) {
      uint32_t null_multiplier =
          bit_util::GetBit(col_non_null_bits, irow + cols[ivarbinary].bit_offset(0)) ? 1
                                                                                     : 0;
      length *= null_multiplier;
    }
    uint32_t* row = reinterpret_cast<uint32_t*>(row_base + row_offsets[i]);
    if (is_first_varbinary) {
      row[0] = rows->metadata().fixed_length + length;
    } else {
      row[0] = row[-1] +
               RowTableMetadata::padding_for_alignment(
                   row[-1], rows->metadata().string_alignment) +
               length;
    }
  }
}

void EncoderOffsets::EncodeSelected(RowTableImpl* rows,
                                    const std::vector<KeyColumnArray>& cols,
                                    uint32_t num_selected, const uint16_t* selection) {
  if (rows->metadata().is_fixed_length) {
    return;
  }
  uint32_t ivarbinary = 0;
  for (size_t icol = 0; icol < cols.size(); ++icol) {
    if (!cols[icol].metadata().is_fixed_length) {
      const uint8_t* non_null_bits = cols[icol].data(0);
      if (non_null_bits && ivarbinary == 0) {
        EncodeSelectedImp<true, true>(ivarbinary, rows, cols, num_selected, selection);
      } else if (non_null_bits && ivarbinary > 0) {
        EncodeSelectedImp<true, false>(ivarbinary, rows, cols, num_selected, selection);
      } else if (!non_null_bits && ivarbinary == 0) {
        EncodeSelectedImp<false, true>(ivarbinary, rows, cols, num_selected, selection);
      } else {
        EncodeSelectedImp<false, false>(ivarbinary, rows, cols, num_selected, selection);
      }
      ivarbinary++;
    }
  }
}

void EncoderVarBinary::Decode(uint32_t start_row, uint32_t num_rows,
                              uint32_t varbinary_col_id, const RowTableImpl& rows,
                              KeyColumnArray* col, LightContext* ctx) {

#if defined(ARROW_HAVE_AVX2)
  if (ctx->has_avx2()) {
    DecodeHelper_avx2(start_row, num_rows, varbinary_col_id, rows, col);
  } else {
#endif
    if (varbinary_col_id == 0) {
      DecodeImp<true>(start_row, num_rows, varbinary_col_id, rows, col);
    } else {
      DecodeImp<false>(start_row, num_rows, varbinary_col_id, rows, col);
    }
#if defined(ARROW_HAVE_AVX2)
  }
#endif
}

template <bool first_varbinary_col>
void EncoderVarBinary::DecodeImp(uint32_t start_row, uint32_t num_rows,
                                 uint32_t varbinary_col_id, const RowTableImpl& rows,
                                 KeyColumnArray* col) {
  DecodeHelper<first_varbinary_col>(
      start_row, num_rows, varbinary_col_id, &rows, nullptr, col, col,
      [](uint8_t* dst, const uint8_t* src, int64_t length) {
        for (uint32_t istripe = 0; istripe < bit_util::CeilDiv(length, 8); ++istripe) {
          auto dst64 = reinterpret_cast<uint64_t*>(dst);
          auto src64 = reinterpret_cast<const uint64_t*>(src);
          util::SafeStore(dst64 + istripe, src64[istripe]);
        }
      });
}

void EncoderNulls::Decode(uint32_t start_row, uint32_t num_rows, const RowTableImpl& rows,
                          std::vector<KeyColumnArray>* cols) {

  DCHECK_GT(cols->size(), 0);
  for (auto& col : *cols) {
    DCHECK(col.length() == num_rows);
    DCHECK(col.mutable_data(0) || col.metadata().is_null_type);
  }

  const uint8_t* null_masks = rows.null_masks();
  uint32_t null_masks_bytes_per_row = rows.metadata().null_masks_bytes_per_row;
  for (size_t col = 0; col < cols->size(); ++col) {
    if ((*cols)[col].metadata().is_null_type) {
      continue;
    }
    uint8_t* non_nulls = (*cols)[col].mutable_data(0);
    const int bit_offset = (*cols)[col].bit_offset(0);
    DCHECK_LT(bit_offset, 8);
    non_nulls[0] |= 0xff << (bit_offset);
    if (bit_offset + num_rows > 8) {
      int bits_in_first_byte = 8 - bit_offset;
      memset(non_nulls + 1, 0xff, bit_util::BytesForBits(num_rows - bits_in_first_byte));
    }
    for (uint32_t row = 0; row < num_rows; ++row) {
      uint32_t null_masks_bit_id =
          (start_row + row) * null_masks_bytes_per_row * 8 + static_cast<uint32_t>(col);
      bool is_set = bit_util::GetBit(null_masks, null_masks_bit_id);
      if (is_set) {
        bit_util::ClearBit(non_nulls, bit_offset + row);
      }
    }
  }
}

void EncoderVarBinary::EncodeSelected(uint32_t ivarbinary, RowTableImpl* rows,
                                      const KeyColumnArray& cols, uint32_t num_selected,
                                      const uint16_t* selection) {
  const uint32_t* row_offsets = rows->offsets();
  uint8_t* row_base = rows->mutable_data(2);
  const uint32_t* col_offsets = cols.offsets();
  const uint8_t* col_base = cols.data(2);

  if (ivarbinary == 0) {
    for (uint32_t i = 0; i < num_selected; ++i) {
      uint8_t* row = row_base + row_offsets[i];
      uint32_t row_offset;
      uint32_t length;
      rows->metadata().first_varbinary_offset_and_length(row, &row_offset, &length);
      uint32_t irow = selection[i];
      memcpy(row + row_offset, col_base + col_offsets[irow], length);
    }
  } else {
    for (uint32_t i = 0; i < num_selected; ++i) {
      uint8_t* row = row_base + row_offsets[i];
      uint32_t row_offset;
      uint32_t length;
      rows->metadata().nth_varbinary_offset_and_length(row, ivarbinary, &row_offset,
                                                       &length);
      uint32_t irow = selection[i];
      memcpy(row + row_offset, col_base + col_offsets[irow], length);
    }
  }
}

void EncoderNulls::EncodeSelected(RowTableImpl* rows,
                                  const std::vector<KeyColumnArray>& cols,
                                  uint32_t num_selected, const uint16_t* selection) {
  uint8_t* null_masks = rows->null_masks();
  uint32_t null_mask_num_bytes = rows->metadata().null_masks_bytes_per_row;
  memset(null_masks, 0, null_mask_num_bytes * num_selected);
  for (size_t icol = 0; icol < cols.size(); ++icol) {
    const uint8_t* non_null_bits = cols[icol].data(0);
    if (non_null_bits) {
      for (uint32_t i = 0; i < num_selected; ++i) {
        uint32_t irow = selection[i];
        bool is_null = !bit_util::GetBit(non_null_bits, irow + cols[icol].bit_offset(0));
        if (is_null) {
          bit_util::SetBit(null_masks, i * null_mask_num_bytes * 8 + icol);
        }
      }
    }
  }
}

}  
}
// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

#include "arrow/compute/row/encode_internal.h"

namespace arrow {
namespace compute {

void RowTableEncoder::Init(const std::vector<KeyColumnMetadata>& cols, LightContext* ctx,
                           int row_alignment, int string_alignment) {
  ctx_ = ctx;
  row_metadata_.FromColumnMetadataVector(cols, row_alignment, string_alignment);
  uint32_t num_cols = row_metadata_.num_cols();
  uint32_t num_varbinary_cols = row_metadata_.num_varbinary_cols();
  batch_all_cols_.resize(num_cols);
  batch_varbinary_cols_.resize(num_varbinary_cols);
  batch_varbinary_cols_base_offsets_.resize(num_varbinary_cols);
}

void RowTableEncoder::PrepareKeyColumnArrays(int64_t start_row, int64_t num_rows,
                                             const std::vector<KeyColumnArray>& cols_in) {
  const auto num_cols = static_cast<uint32_t>(cols_in.size());
  DCHECK(batch_all_cols_.size() == num_cols);

  uint32_t num_varbinary_visited = 0;
  for (uint32_t i = 0; i < num_cols; ++i) {
    const KeyColumnArray& col = cols_in[row_metadata_.column_order[i]];
    KeyColumnArray col_window = col.Slice(start_row, num_rows);

    batch_all_cols_[i] = col_window;
    if (!col.metadata().is_fixed_length) {
      DCHECK(num_varbinary_visited < batch_varbinary_cols_.size());
      // If start row is zero, then base offset of varbinary column is also zero.
      if (start_row == 0) {
        batch_varbinary_cols_base_offsets_[num_varbinary_visited] = 0;
      } else {
        batch_varbinary_cols_base_offsets_[num_varbinary_visited] =
            col.offsets()[start_row];
      }
      batch_varbinary_cols_[num_varbinary_visited++] = col_window;
    }
  }
}

void RowTableEncoder::DecodeFixedLengthBuffers(int64_t start_row_input,
                                               int64_t start_row_output, int64_t num_rows,
                                               const RowTableImpl& rows,
                                               std::vector<KeyColumnArray>* cols) {
  // Prepare column array vectors
  PrepareKeyColumnArrays(start_row_output, num_rows, *cols);

  // Create two temp vectors with 16-bit elements
  auto temp_buffer_holder_A =
      util::TempVectorHolder<uint16_t>(ctx_->stack, static_cast<uint32_t>(num_rows));
  auto temp_buffer_A = KeyColumnArray(
      KeyColumnMetadata(true, sizeof(uint16_t)), num_rows, nullptr,
      reinterpret_cast<uint8_t*>(temp_buffer_holder_A.mutable_data()), nullptr);
  auto temp_buffer_holder_B =
      util::TempVectorHolder<uint16_t>(ctx_->stack, static_cast<uint32_t>(num_rows));
  auto temp_buffer_B = KeyColumnArray(
      KeyColumnMetadata(true, sizeof(uint16_t)), num_rows, nullptr,
      reinterpret_cast<uint8_t*>(temp_buffer_holder_B.mutable_data()), nullptr);

  bool is_row_fixed_length = row_metadata_.is_fixed_length;
  if (!is_row_fixed_length) {
    EncoderOffsets::Decode(static_cast<uint32_t>(start_row_input),
                           static_cast<uint32_t>(num_rows), rows, &batch_varbinary_cols_,
                           batch_varbinary_cols_base_offsets_, ctx_);
  }

  // Process fixed length columns
  const auto num_cols = static_cast<uint32_t>(batch_all_cols_.size());
  for (uint32_t i = 0; i < num_cols;) {
    if (!batch_all_cols_[i].metadata().is_fixed_length ||
        batch_all_cols_[i].metadata().is_null_type) {
      i += 1;
      continue;
    }
    bool can_process_pair =
        (i + 1 < num_cols) && batch_all_cols_[i + 1].metadata().is_fixed_length &&
        EncoderBinaryPair::CanProcessPair(batch_all_cols_[i].metadata(),
                                          batch_all_cols_[i + 1].metadata());
    if (!can_process_pair) {
      EncoderBinary::Decode(static_cast<uint32_t>(start_row_input),
                            static_cast<uint32_t>(num_rows),
                            row_metadata_.column_offsets[i], rows, &batch_all_cols_[i],
                            ctx_, &temp_buffer_A);
      i += 1;
    } else {
      EncoderBinaryPair::Decode(
          static_cast<uint32_t>(start_row_input), static_cast<uint32_t>(num_rows),
          row_metadata_.column_offsets[i], rows, &batch_all_cols_[i],
          &batch_all_cols_[i + 1], ctx_, &temp_buffer_A, &temp_buffer_B);
      i += 2;
    }
  }

  // Process nulls
  EncoderNulls::Decode(static_cast<uint32_t>(start_row_input),
                       static_cast<uint32_t>(num_rows), rows, &batch_all_cols_);
}

void RowTableEncoder::DecodeVaryingLengthBuffers(int64_t start_row_input,
                                                 int64_t start_row_output,
                                                 int64_t num_rows,
                                                 const RowTableImpl& rows,
                                                 std::vector<KeyColumnArray>* cols) {
  // Prepare column array vectors
  PrepareKeyColumnArrays(start_row_output, num_rows, *cols);

  bool is_row_fixed_length = row_metadata_.is_fixed_length;
  if (!is_row_fixed_length) {
    for (size_t i = 0; i < batch_varbinary_cols_.size(); ++i) {
      // Memcpy varbinary fields into precomputed in the previous step
      // positions in the output row buffer.
      EncoderVarBinary::Decode(static_cast<uint32_t>(start_row_input),
                               static_cast<uint32_t>(num_rows), static_cast<uint32_t>(i),
                               rows, &batch_varbinary_cols_[i], ctx_);
    }
  }
}

void RowTableEncoder::PrepareEncodeSelected(int64_t start_row, int64_t num_rows,
                                            const std::vector<KeyColumnArray>& cols) {
  // Prepare column array vectors
  PrepareKeyColumnArrays(start_row, num_rows, cols);
}

Status RowTableEncoder::EncodeSelected(RowTableImpl* rows, uint32_t num_selected,
                                       const uint16_t* selection) {
  rows->Clean();
  RETURN_NOT_OK(
      rows->AppendEmpty(static_cast<uint32_t>(num_selected), static_cast<uint32_t>(0)));

  EncoderOffsets::GetRowOffsetsSelected(rows, batch_varbinary_cols_, num_selected,
                                        selection);

  RETURN_NOT_OK(rows->AppendEmpty(static_cast<uint32_t>(0),
                                  static_cast<uint32_t>(rows->offsets()[num_selected])));

  for (size_t icol = 0; icol < batch_all_cols_.size(); ++icol) {
    if (batch_all_cols_[icol].metadata().is_fixed_length) {
      uint32_t offset_within_row = rows->metadata().column_offsets[icol];
      EncoderBinary::EncodeSelected(offset_within_row, rows, batch_all_cols_[icol],
                                    num_selected, selection);
    }
  }

  EncoderOffsets::EncodeSelected(rows, batch_varbinary_cols_, num_selected, selection);

  for (size_t icol = 0; icol < batch_varbinary_cols_.size(); ++icol) {
    EncoderVarBinary::EncodeSelected(static_cast<uint32_t>(icol), rows,
                                     batch_varbinary_cols_[icol], num_selected,
                                     selection);
  }

  EncoderNulls::EncodeSelected(rows, batch_all_cols_, num_selected, selection);

  return Status::OK();
}

namespace {
struct TransformBoolean {
  static KeyColumnArray ArrayReplace(const KeyColumnArray& column,
                                     const KeyColumnArray& temp) {
    // Make sure that the temp buffer is large enough
    DCHECK(temp.length() >= column.length() && temp.metadata().is_fixed_length &&
           temp.metadata().fixed_length >= sizeof(uint8_t));
    KeyColumnMetadata metadata;
    metadata.is_fixed_length = true;
    metadata.fixed_length = sizeof(uint8_t);
    constexpr int buffer_index = 1;
    return column.WithBufferFrom(temp, buffer_index).WithMetadata(metadata);
  }

  static void PostDecode(const KeyColumnArray& input, KeyColumnArray* output,
                         LightContext* ctx) {
    // Make sure that metadata and lengths are compatible.
    DCHECK(output->metadata().is_fixed_length == input.metadata().is_fixed_length);
    DCHECK(output->metadata().fixed_length == 0 && input.metadata().fixed_length == 1);
    DCHECK(output->length() == input.length());
    constexpr int buffer_index = 1;
    DCHECK(input.data(buffer_index) != nullptr);
    DCHECK(output->mutable_data(buffer_index) != nullptr);

    util::bit_util::bytes_to_bits(
        ctx->hardware_flags, static_cast<int>(input.length()), input.data(buffer_index),
        output->mutable_data(buffer_index), output->bit_offset(buffer_index));
  }
};

}  // namespace

bool EncoderInteger::IsBoolean(const KeyColumnMetadata& metadata) {
  return metadata.is_fixed_length && metadata.fixed_length == 0 && !metadata.is_null_type;
}

bool EncoderInteger::UsesTransform(const KeyColumnArray& column) {
  return IsBoolean(column.metadata());
}

KeyColumnArray EncoderInteger::ArrayReplace(const KeyColumnArray& column,
                                            const KeyColumnArray& temp) {
  if (IsBoolean(column.metadata())) {
    return TransformBoolean::ArrayReplace(column, temp);
  }
  return column;
}

void EncoderInteger::PostDecode(const KeyColumnArray& input, KeyColumnArray* output,
                                LightContext* ctx) {
  if (IsBoolean(output->metadata())) {
    TransformBoolean::PostDecode(input, output, ctx);
  }
}

void EncoderInteger::Decode(uint32_t start_row, uint32_t num_rows,
                            uint32_t offset_within_row, const RowTableImpl& rows,
                            KeyColumnArray* col, LightContext* ctx,
                            KeyColumnArray* temp) {
  KeyColumnArray col_prep;
  if (UsesTransform(*col)) {
    col_prep = ArrayReplace(*col, *temp);
  } else {
    col_prep = *col;
  }

  // When we have a single fixed length column we can just do memcpy
  if (rows.metadata().is_fixed_length &&
      col_prep.metadata().fixed_length == rows.metadata().fixed_length) {
    DCHECK_EQ(offset_within_row, 0);
    uint32_t row_size = rows.metadata().fixed_length;
    memcpy(col_prep.mutable_data(1), rows.data(1) + start_row * row_size,
           num_rows * row_size);
  } else if (rows.metadata().is_fixed_length) {
    uint32_t row_size = rows.metadata().fixed_length;
    const uint8_t* row_base = rows.data(1) + start_row * row_size;
    row_base += offset_within_row;
    uint8_t* col_base = col_prep.mutable_data(1);
    switch (col_prep.metadata().fixed_length) {
      case 1:
        for (uint32_t i = 0; i < num_rows; ++i) {
          col_base[i] = row_base[i * row_size];
        }
        break;
      case 2:
        for (uint32_t i = 0; i < num_rows; ++i) {
          reinterpret_cast<uint16_t*>(col_base)[i] =
              *reinterpret_cast<const uint16_t*>(row_base + i * row_size);
        }
        break;
      case 4:
        for (uint32_t i = 0; i < num_rows; ++i) {
          reinterpret_cast<uint32_t*>(col_base)[i] =
              *reinterpret_cast<const uint32_t*>(row_base + i * row_size);
        }
        break;
      case 8:
        for (uint32_t i = 0; i < num_rows; ++i) {
          reinterpret_cast<uint64_t*>(col_base)[i] =
              *reinterpret_cast<const uint64_t*>(row_base + i * row_size);
        }
        break;
      default:
        DCHECK(false);
    }
  } else {
    const uint32_t* row_offsets = rows.offsets() + start_row;
    const uint8_t* row_base = rows.data(2);
    row_base += offset_within_row;
    uint8_t* col_base = col_prep.mutable_data(1);
    switch (col_prep.metadata().fixed_length) {
      case 1:
        for (uint32_t i = 0; i < num_rows; ++i) {
          col_base[i] = row_base[row_offsets[i]];
        }
        break;
      case 2:
        for (uint32_t i = 0; i < num_rows; ++i) {
          reinterpret_cast<uint16_t*>(col_base)[i] =
              *reinterpret_cast<const uint16_t*>(row_base + row_offsets[i]);
        }
        break;
      case 4:
        for (uint32_t i = 0; i < num_rows; ++i) {
          reinterpret_cast<uint32_t*>(col_base)[i] =
              *reinterpret_cast<const uint32_t*>(row_base + row_offsets[i]);
        }
        break;
      case 8:
        for (uint32_t i = 0; i < num_rows; ++i) {
          reinterpret_cast<uint64_t*>(col_base)[i] =
              *reinterpret_cast<const uint64_t*>(row_base + row_offsets[i]);
        }
        break;
      default:
        DCHECK(false);
    }
  }

  if (UsesTransform(*col)) {
    PostDecode(col_prep, col, ctx);
  }
}

template <class COPY_FN, class SET_NULL_FN>
void EncoderBinary::EncodeSelectedImp(uint32_t offset_within_row, RowTableImpl* rows,
                                      const KeyColumnArray& col, uint32_t num_selected,
                                      const uint16_t* selection, COPY_FN copy_fn,
                                      SET_NULL_FN set_null_fn) {
  bool is_fixed_length = rows->metadata().is_fixed_length;
  if (is_fixed_length) {
    uint32_t row_width = rows->metadata().fixed_length;
    const uint8_t* src_base = col.data(1);
    uint8_t* dst = rows->mutable_data(1) + offset_within_row;
    for (uint32_t i = 0; i < num_selected; ++i) {
      copy_fn(dst, src_base, selection[i]);
      dst += row_width;
    }
    if (col.data(0)) {
      const uint8_t* non_null_bits = col.data(0);
      uint8_t* dst = rows->mutable_data(1) + offset_within_row;
      for (uint32_t i = 0; i < num_selected; ++i) {
        bool is_null = !bit_util::GetBit(non_null_bits, selection[i] + col.bit_offset(0));
        if (is_null) {
          set_null_fn(dst);
        }
        dst += row_width;
      }
    }
  } else {
    const uint8_t* src_base = col.data(1);
    uint8_t* dst = rows->mutable_data(2) + offset_within_row;
    const uint32_t* offsets = rows->offsets();
    for (uint32_t i = 0; i < num_selected; ++i) {
      copy_fn(dst + offsets[i], src_base, selection[i]);
    }
    if (col.data(0)) {
      const uint8_t* non_null_bits = col.data(0);
      uint8_t* dst = rows->mutable_data(2) + offset_within_row;
      const uint32_t* offsets = rows->offsets();
      for (uint32_t i = 0; i < num_selected; ++i) {
        bool is_null = !bit_util::GetBit(non_null_bits, selection[i] + col.bit_offset(0));
        if (is_null) {
          set_null_fn(dst + offsets[i]);
        }
      }
    }
  }
}

void EncoderBinary::EncodeSelected(uint32_t offset_within_row, RowTableImpl* rows,
                                   const KeyColumnArray& col, uint32_t num_selected,
                                   const uint16_t* selection) {
  if (col.metadata().is_null_type) {
    return;
  }
  uint32_t col_width = col.metadata().fixed_length;
  if (col_width == 0) {
    int bit_offset = col.bit_offset(1);
    EncodeSelectedImp(
        offset_within_row, rows, col, num_selected, selection,
        [bit_offset](uint8_t* dst, const uint8_t* src_base, uint16_t irow) {
          *dst = bit_util::GetBit(src_base, irow + bit_offset) ? 0xff : 0x00;
        },
        [](uint8_t* dst) { *dst = 0xae; });
  } else if (col_width == 1) {
    EncodeSelectedImp(
        offset_within_row, rows, col, num_selected, selection,
        [](uint8_t* dst, const uint8_t* src_base, uint16_t irow) {
          *dst = src_base[irow];
        },
        [](uint8_t* dst) { *dst = 0xae; });
  } else if (col_width == 2) {
    EncodeSelectedImp(
        offset_within_row, rows, col, num_selected, selection,
        [](uint8_t* dst, const uint8_t* src_base, uint16_t irow) {
          *reinterpret_cast<uint16_t*>(dst) =
              reinterpret_cast<const uint16_t*>(src_base)[irow];
        },
        [](uint8_t* dst) { *reinterpret_cast<uint16_t*>(dst) = 0xaeae; });
  } else if (col_width == 4) {
    EncodeSelectedImp(
        offset_within_row, rows, col, num_selected, selection,
        [](uint8_t* dst, const uint8_t* src_base, uint16_t irow) {
          *reinterpret_cast<uint32_t*>(dst) =
              reinterpret_cast<const uint32_t*>(src_base)[irow];
        },
        [](uint8_t* dst) {
          *reinterpret_cast<uint32_t*>(dst) = static_cast<uint32_t>(0xaeaeaeae);
        });
  } else if (col_width == 8) {
    EncodeSelectedImp(
        offset_within_row, rows, col, num_selected, selection,
        [](uint8_t* dst, const uint8_t* src_base, uint16_t irow) {
          *reinterpret_cast<uint64_t*>(dst) =
              reinterpret_cast<const uint64_t*>(src_base)[irow];
        },
        [](uint8_t* dst) { *reinterpret_cast<uint64_t*>(dst) = 0xaeaeaeaeaeaeaeaeULL; });
  } else {
    EncodeSelectedImp(
        offset_within_row, rows, col, num_selected, selection,
        [col_width](uint8_t* dst, const uint8_t* src_base, uint16_t irow) {
          memcpy(dst, src_base + col_width * irow, col_width);
        },
        [col_width](uint8_t* dst) { memset(dst, 0xae, col_width); });
  }
}

bool EncoderBinary::IsInteger(const KeyColumnMetadata& metadata) {
  if (metadata.is_null_type) {
    return false;
  }
  bool is_fixed_length = metadata.is_fixed_length;
  auto size = metadata.fixed_length;
  return is_fixed_length &&
         (size == 0 || size == 1 || size == 2 || size == 4 || size == 8);
}

void EncoderBinary::Decode(uint32_t start_row, uint32_t num_rows,
                           uint32_t offset_within_row, const RowTableImpl& rows,
                           KeyColumnArray* col, LightContext* ctx, KeyColumnArray* temp) {
  if (IsInteger(col->metadata())) {
    EncoderInteger::Decode(start_row, num_rows, offset_within_row, rows, col, ctx, temp);
  } else {
    KeyColumnArray col_prep;
    if (EncoderInteger::UsesTransform(*col)) {
      col_prep = EncoderInteger::ArrayReplace(*col, *temp);
    } else {
      col_prep = *col;
    }

    bool is_row_fixed_length = rows.metadata().is_fixed_length;

#if defined(ARROW_HAVE_AVX2)
    if (ctx->has_avx2()) {
      DecodeHelper_avx2(is_row_fixed_length, start_row, num_rows, offset_within_row, rows,
                        col);
    } else {
#endif
      if (is_row_fixed_length) {
        DecodeImp<true>(start_row, num_rows, offset_within_row, rows, col);
      } else {
        DecodeImp<false>(start_row, num_rows, offset_within_row, rows, col);
      }
#if defined(ARROW_HAVE_AVX2)
    }
#endif

    if (EncoderInteger::UsesTransform(*col)) {
      EncoderInteger::PostDecode(col_prep, col, ctx);
    }
  }
}

template <bool is_row_fixed_length>
void EncoderBinary::DecodeImp(uint32_t start_row, uint32_t num_rows,
                              uint32_t offset_within_row, const RowTableImpl& rows,
                              KeyColumnArray* col) {
  DecodeHelper<is_row_fixed_length>(
      start_row, num_rows, offset_within_row, &rows, nullptr, col, col,
      [](uint8_t* dst, const uint8_t* src, int64_t length) {
        for (uint32_t istripe = 0; istripe < bit_util::CeilDiv(length, 8); ++istripe) {
          auto dst64 = reinterpret_cast<uint64_t*>(dst);
          auto src64 = reinterpret_cast<const uint64_t*>(src);
          util::SafeStore(dst64 + istripe, src64[istripe]);
        }
      });
}

void EncoderBinaryPair::Decode(uint32_t start_row, uint32_t num_rows,
                               uint32_t offset_within_row, const RowTableImpl& rows,
                               KeyColumnArray* col1, KeyColumnArray* col2,
                               LightContext* ctx, KeyColumnArray* temp1,
                               KeyColumnArray* temp2) {
  DCHECK(CanProcessPair(col1->metadata(), col2->metadata()));

  KeyColumnArray col_prep[2];
  if (EncoderInteger::UsesTransform(*col1)) {
    col_prep[0] = EncoderInteger::ArrayReplace(*col1, *temp1);
  } else {
    col_prep[0] = *col1;
  }
  if (EncoderInteger::UsesTransform(*col2)) {
    col_prep[1] = EncoderInteger::ArrayReplace(*col2, *temp2);
  } else {
    col_prep[1] = *col2;
  }

  uint32_t col_width1 = col_prep[0].metadata().fixed_length;
  uint32_t col_width2 = col_prep[1].metadata().fixed_length;
  int log_col_width1 = col_width1 == 8   ? 3
                       : col_width1 == 4 ? 2
                       : col_width1 == 2 ? 1
                                         : 0;
  int log_col_width2 = col_width2 == 8   ? 3
                       : col_width2 == 4 ? 2
                       : col_width2 == 2 ? 1
                                         : 0;

  bool is_row_fixed_length = rows.metadata().is_fixed_length;

  uint32_t num_processed = 0;
#if defined(ARROW_HAVE_AVX2)
  if (ctx->has_avx2() && col_width1 == col_width2) {
    num_processed =
        DecodeHelper_avx2(is_row_fixed_length, col_width1, start_row, num_rows,
                          offset_within_row, rows, &col_prep[0], &col_prep[1]);
  }
#endif
  if (num_processed < num_rows) {
    using DecodeImp_t = void (*)(uint32_t, uint32_t, uint32_t, uint32_t,
                                 const RowTableImpl&, KeyColumnArray*, KeyColumnArray*);
    static const DecodeImp_t DecodeImp_fn[] = {
        DecodeImp<false, uint8_t, uint8_t>,   DecodeImp<false, uint16_t, uint8_t>,
        DecodeImp<false, uint32_t, uint8_t>,  DecodeImp<false, uint64_t, uint8_t>,
        DecodeImp<false, uint8_t, uint16_t>,  DecodeImp<false, uint16_t, uint16_t>,
        DecodeImp<false, uint32_t, uint16_t>, DecodeImp<false, uint64_t, uint16_t>,
        DecodeImp<false, uint8_t, uint32_t>,  DecodeImp<false, uint16_t, uint32_t>,
        DecodeImp<false, uint32_t, uint32_t>, DecodeImp<false, uint64_t, uint32_t>,
        DecodeImp<false, uint8_t, uint64_t>,  DecodeImp<false, uint16_t, uint64_t>,
        DecodeImp<false, uint32_t, uint64_t>, DecodeImp<false, uint64_t, uint64_t>,
        DecodeImp<true, uint8_t, uint8_t>,    DecodeImp<true, uint16_t, uint8_t>,
        DecodeImp<true, uint32_t, uint8_t>,   DecodeImp<true, uint64_t, uint8_t>,
        DecodeImp<true, uint8_t, uint16_t>,   DecodeImp<true, uint16_t, uint16_t>,
        DecodeImp<true, uint32_t, uint16_t>,  DecodeImp<true, uint64_t, uint16_t>,
        DecodeImp<true, uint8_t, uint32_t>,   DecodeImp<true, uint16_t, uint32_t>,
        DecodeImp<true, uint32_t, uint32_t>,  DecodeImp<true, uint64_t, uint32_t>,
        DecodeImp<true, uint8_t, uint64_t>,   DecodeImp<true, uint16_t, uint64_t>,
        DecodeImp<true, uint32_t, uint64_t>,  DecodeImp<true, uint64_t, uint64_t>};
    int dispatch_const =
        (log_col_width2 << 2) | log_col_width1 | (is_row_fixed_length ? 16 : 0);
    DecodeImp_fn[dispatch_const](num_processed, start_row, num_rows, offset_within_row,
                                 rows, &(col_prep[0]), &(col_prep[1]));
  }

  if (EncoderInteger::UsesTransform(*col1)) {
    EncoderInteger::PostDecode(col_prep[0], col1, ctx);
  }
  if (EncoderInteger::UsesTransform(*col2)) {
    EncoderInteger::PostDecode(col_prep[1], col2, ctx);
  }
}

template <bool is_row_fixed_length, typename col1_type, typename col2_type>
void EncoderBinaryPair::DecodeImp(uint32_t num_rows_to_skip, uint32_t start_row,
                                  uint32_t num_rows, uint32_t offset_within_row,
                                  const RowTableImpl& rows, KeyColumnArray* col1,
                                  KeyColumnArray* col2) {
  DCHECK(rows.length() >= start_row + num_rows);
  DCHECK(col1->length() == num_rows && col2->length() == num_rows);

  uint8_t* dst_A = col1->mutable_data(1);
  uint8_t* dst_B = col2->mutable_data(1);

  uint32_t fixed_length = rows.metadata().fixed_length;
  const uint32_t* offsets;
  const uint8_t* src_base;
  if (is_row_fixed_length) {
    src_base = rows.data(1) + fixed_length * start_row + offset_within_row;
    offsets = nullptr;
  } else {
    src_base = rows.data(2) + offset_within_row;
    offsets = rows.offsets() + start_row;
  }

  using col1_type_const = typename std::add_const<col1_type>::type;
  using col2_type_const = typename std::add_const<col2_type>::type;

  if (is_row_fixed_length) {
    const uint8_t* src = src_base + num_rows_to_skip * fixed_length;
    for (uint32_t i = num_rows_to_skip; i < num_rows; ++i) {
      reinterpret_cast<col1_type*>(dst_A)[i] = *reinterpret_cast<col1_type_const*>(src);
      reinterpret_cast<col2_type*>(dst_B)[i] =
          *reinterpret_cast<col2_type_const*>(src + sizeof(col1_type));
      src += fixed_length;
    }
  } else {
    for (uint32_t i = num_rows_to_skip; i < num_rows; ++i) {
      const uint8_t* src = src_base + offsets[i];
      reinterpret_cast<col1_type*>(dst_A)[i] = *reinterpret_cast<col1_type_const*>(src);
      reinterpret_cast<col2_type*>(dst_B)[i] =
          *reinterpret_cast<col2_type_const*>(src + sizeof(col1_type));
    }
  }
}

void EncoderOffsets::Decode(uint32_t start_row, uint32_t num_rows,
                            const RowTableImpl& rows,
                            std::vector<KeyColumnArray>* varbinary_cols,
                            const std::vector<uint32_t>& varbinary_cols_base_offset,
                            LightContext* ctx) {
  DCHECK(!varbinary_cols->empty());
  DCHECK(varbinary_cols->size() == varbinary_cols_base_offset.size());

  DCHECK(!rows.metadata().is_fixed_length);
  DCHECK(rows.length() >= start_row + num_rows);
  for (const auto& col : *varbinary_cols) {
    // Rows and columns must all be varying-length
    DCHECK(!col.metadata().is_fixed_length);
    // The space in columns must be exactly equal to a subset of rows selected
    DCHECK(col.length() == num_rows);
  }

  // Offsets of varbinary columns data within each encoded row are stored
  // in the same encoded row as an array of 32-bit integers.
  // This array follows immediately the data of fixed-length columns.
  // There is one element for each varying-length column.
  // The Nth element is the sum of all the lengths of varbinary columns data in
  // that row, up to and including Nth varbinary column.

  const uint32_t* row_offsets = rows.offsets() + start_row;

  // Set the base offset for each column
  for (size_t col = 0; col < varbinary_cols->size(); ++col) {
    uint32_t* col_offsets = (*varbinary_cols)[col].mutable_offsets();
    col_offsets[0] = varbinary_cols_base_offset[col];
  }

  int string_alignment = rows.metadata().string_alignment;

  for (uint32_t i = 0; i < num_rows; ++i) {
    // Find the beginning of cumulative lengths array for next row
    const uint8_t* row = rows.data(2) + row_offsets[i];
    const uint32_t* varbinary_ends = rows.metadata().varbinary_end_array(row);

    // Update the offset of each column
    uint32_t offset_within_row = rows.metadata().fixed_length;
    for (size_t col = 0; col < varbinary_cols->size(); ++col) {
      offset_within_row +=
          RowTableMetadata::padding_for_alignment(offset_within_row, string_alignment);
      uint32_t length = varbinary_ends[col] - offset_within_row;
      offset_within_row = varbinary_ends[col];
      uint32_t* col_offsets = (*varbinary_cols)[col].mutable_offsets();
      col_offsets[i + 1] = col_offsets[i] + length;
    }
  }
}

void EncoderOffsets::GetRowOffsetsSelected(RowTableImpl* rows,
                                           const std::vector<KeyColumnArray>& cols,
                                           uint32_t num_selected,
                                           const uint16_t* selection) {
  if (rows->metadata().is_fixed_length) {
    return;
  }

  uint32_t* row_offsets = rows->mutable_offsets();
  for (uint32_t i = 0; i < num_selected; ++i) {
    row_offsets[i] = rows->metadata().fixed_length;
  }

  for (size_t icol = 0; icol < cols.size(); ++icol) {
    bool is_fixed_length = (cols[icol].metadata().is_fixed_length);
    if (!is_fixed_length) {
      const uint32_t* col_offsets = cols[icol].offsets();
      for (uint32_t i = 0; i < num_selected; ++i) {
        uint32_t irow = selection[i];
        uint32_t length = col_offsets[irow + 1] - col_offsets[irow];
        row_offsets[i] += RowTableMetadata::padding_for_alignment(
            row_offsets[i], rows->metadata().string_alignment);
        row_offsets[i] += length;
      }
      const uint8_t* non_null_bits = cols[icol].data(0);
      if (non_null_bits) {
        const uint32_t* col_offsets = cols[icol].offsets();
        for (uint32_t i = 0; i < num_selected; ++i) {
          uint32_t irow = selection[i];
          bool is_null =
              !bit_util::GetBit(non_null_bits, irow + cols[icol].bit_offset(0));
          if (is_null) {
            uint32_t length = col_offsets[irow + 1] - col_offsets[irow];
            row_offsets[i] -= length;
          }
        }
      }
    }
  }

  uint32_t sum = 0;
  int row_alignment = rows->metadata().row_alignment;
  for (uint32_t i = 0; i < num_selected; ++i) {
    uint32_t length = row_offsets[i];
    length += RowTableMetadata::padding_for_alignment(length, row_alignment);
    row_offsets[i] = sum;
    sum += length;
  }
  row_offsets[num_selected] = sum;
}

template <bool has_nulls, bool is_first_varbinary>
void EncoderOffsets::EncodeSelectedImp(uint32_t ivarbinary, RowTableImpl* rows,
                                       const std::vector<KeyColumnArray>& cols,
                                       uint32_t num_selected, const uint16_t* selection) {
  const uint32_t* row_offsets = rows->offsets();
  uint8_t* row_base = rows->mutable_data(2) +
                      rows->metadata().varbinary_end_array_offset +
                      ivarbinary * sizeof(uint32_t);
  const uint32_t* col_offsets = cols[ivarbinary].offsets();
  const uint8_t* col_non_null_bits = cols[ivarbinary].data(0);

  for (uint32_t i = 0; i < num_selected; ++i) {
    uint32_t irow = selection[i];
    uint32_t length = col_offsets[irow + 1] - col_offsets[irow];
    if (has_nulls) {
      uint32_t null_multiplier =
          bit_util::GetBit(col_non_null_bits, irow + cols[ivarbinary].bit_offset(0)) ? 1
                                                                                     : 0;
      length *= null_multiplier;
    }
    uint32_t* row = reinterpret_cast<uint32_t*>(row_base + row_offsets[i]);
    if (is_first_varbinary) {
      row[0] = rows->metadata().fixed_length + length;
    } else {
      row[0] = row[-1] +
               RowTableMetadata::padding_for_alignment(
                   row[-1], rows->metadata().string_alignment) +
               length;
    }
  }
}

void EncoderOffsets::EncodeSelected(RowTableImpl* rows,
                                    const std::vector<KeyColumnArray>& cols,
                                    uint32_t num_selected, const uint16_t* selection) {
  if (rows->metadata().is_fixed_length) {
    return;
  }
  uint32_t ivarbinary = 0;
  for (size_t icol = 0; icol < cols.size(); ++icol) {
    if (!cols[icol].metadata().is_fixed_length) {
      const uint8_t* non_null_bits = cols[icol].data(0);
      if (non_null_bits && ivarbinary == 0) {
        EncodeSelectedImp<true, true>(ivarbinary, rows, cols, num_selected, selection);
      } else if (non_null_bits && ivarbinary > 0) {
        EncodeSelectedImp<true, false>(ivarbinary, rows, cols, num_selected, selection);
      } else if (!non_null_bits && ivarbinary == 0) {
        EncodeSelectedImp<false, true>(ivarbinary, rows, cols, num_selected, selection);
      } else {
        EncodeSelectedImp<false, false>(ivarbinary, rows, cols, num_selected, selection);
      }
      ivarbinary++;
    }
  }
}

void EncoderVarBinary::Decode(uint32_t start_row, uint32_t num_rows,
                              uint32_t varbinary_col_id, const RowTableImpl& rows,
                              KeyColumnArray* col, LightContext* ctx) {
  // Output column varbinary buffer needs an extra 32B
  // at the end in avx2 version and 8B otherwise.
#if defined(ARROW_HAVE_AVX2)
  if (ctx->has_avx2()) {
    DecodeHelper_avx2(start_row, num_rows, varbinary_col_id, rows, col);
  } else {
#endif
    if (varbinary_col_id == 0) {
      DecodeImp<true>(start_row, num_rows, varbinary_col_id, rows, col);
    } else {
      DecodeImp<false>(start_row, num_rows, varbinary_col_id, rows, col);
    }
#if defined(ARROW_HAVE_AVX2)
  }
#endif
}

template <bool first_varbinary_col>
void EncoderVarBinary::DecodeImp(uint32_t start_row, uint32_t num_rows,
                                 uint32_t varbinary_col_id, const RowTableImpl& rows,
                                 KeyColumnArray* col) {
  DecodeHelper<first_varbinary_col>(
      start_row, num_rows, varbinary_col_id, &rows, nullptr, col, col,
      [](uint8_t* dst, const uint8_t* src, int64_t length) {
        for (uint32_t istripe = 0; istripe < bit_util::CeilDiv(length, 8); ++istripe) {
          auto dst64 = reinterpret_cast<uint64_t*>(dst);
          auto src64 = reinterpret_cast<const uint64_t*>(src);
          util::SafeStore(dst64 + istripe, src64[istripe]);
        }
      });
}

void EncoderNulls::Decode(uint32_t start_row, uint32_t num_rows, const RowTableImpl& rows,
                          std::vector<KeyColumnArray>* cols) {
  // Every output column needs to have a space for exactly the required number
  // of rows. It also needs to have non-nulls bit-vector allocated and mutable.
  DCHECK_GT(cols->size(), 0);
  for (auto& col : *cols) {
    DCHECK(col.length() == num_rows);
    DCHECK(col.mutable_data(0) || col.metadata().is_null_type);
  }

  const uint8_t* null_masks = rows.null_masks();
  uint32_t null_masks_bytes_per_row = rows.metadata().null_masks_bytes_per_row;
  for (size_t col = 0; col < cols->size(); ++col) {
    if ((*cols)[col].metadata().is_null_type) {
      continue;
    }
    uint8_t* non_nulls = (*cols)[col].mutable_data(0);
    const int bit_offset = (*cols)[col].bit_offset(0);
    DCHECK_LT(bit_offset, 8);
    non_nulls[0] |= 0xff << (bit_offset);
    if (bit_offset + num_rows > 8) {
      int bits_in_first_byte = 8 - bit_offset;
      memset(non_nulls + 1, 0xff, bit_util::BytesForBits(num_rows - bits_in_first_byte));
    }
    for (uint32_t row = 0; row < num_rows; ++row) {
      uint32_t null_masks_bit_id =
          (start_row + row) * null_masks_bytes_per_row * 8 + static_cast<uint32_t>(col);
      bool is_set = bit_util::GetBit(null_masks, null_masks_bit_id);
      if (is_set) {
        bit_util::ClearBit(non_nulls, bit_offset + row);
      }
    }
  }
}

void EncoderVarBinary::EncodeSelected(uint32_t ivarbinary, RowTableImpl* rows,
                                      const KeyColumnArray& cols, uint32_t num_selected,
                                      const uint16_t* selection) {
  const uint32_t* row_offsets = rows->offsets();
  uint8_t* row_base = rows->mutable_data(2);
  const uint32_t* col_offsets = cols.offsets();
  const uint8_t* col_base = cols.data(2);

  if (ivarbinary == 0) {
    for (uint32_t i = 0; i < num_selected; ++i) {
      uint8_t* row = row_base + row_offsets[i];
      uint32_t row_offset;
      uint32_t length;
      rows->metadata().first_varbinary_offset_and_length(row, &row_offset, &length);
      uint32_t irow = selection[i];
      memcpy(row + row_offset, col_base + col_offsets[irow], length);
    }
  } else {
    for (uint32_t i = 0; i < num_selected; ++i) {
      uint8_t* row = row_base + row_offsets[i];
      uint32_t row_offset;
      uint32_t length;
      rows->metadata().nth_varbinary_offset_and_length(row, ivarbinary, &row_offset,
                                                       &length);
      uint32_t irow = selection[i];
      memcpy(row + row_offset, col_base + col_offsets[irow], length);
    }
  }
}

void EncoderNulls::EncodeSelected(RowTableImpl* rows,
                                  const std::vector<KeyColumnArray>& cols,
                                  uint32_t num_selected, const uint16_t* selection) {
  uint8_t* null_masks = rows->null_masks();
  uint32_t null_mask_num_bytes = rows->metadata().null_masks_bytes_per_row;
  memset(null_masks, 0, null_mask_num_bytes * num_selected);
  for (size_t icol = 0; icol < cols.size(); ++icol) {
    const uint8_t* non_null_bits = cols[icol].data(0);
    if (non_null_bits) {
      for (uint32_t i = 0; i < num_selected; ++i) {
        uint32_t irow = selection[i];
        bool is_null = !bit_util::GetBit(non_null_bits, irow + cols[icol].bit_offset(0));
        if (is_null) {
          bit_util::SetBit(null_masks, i * null_mask_num_bytes * 8 + icol);
        }
      }
    }
  }
}

}  // namespace compute
}  // namespace arrow
