Function exportValidityBitmap

bolt/vector/arrow/Bridge.cpp:787–830

This functions does two things: (a) sets the value of null_count, and (b) the validity buffer (if there is at least one null row).

// This functions does two things: (a) sets the value of null_count, and (b)
// the validity buffer (if there is at least one null row).
void exportValidityBitmap(
    const BaseVector& vec,
    const Selection& rows,
    const ArrowOptions& options,
    ArrowArray& out,
    memory::MemoryPool* pool,
    BoltToArrowBridgeHolder& holder) {
  if (options.exportToArrowIPC && vec.typeKind() == TypeKind::UNKNOWN) {
    out.null_count = rows.count();
    if (vec.encoding() == VectorEncoding::Simple::DICTIONARY) {
      auto nulls =
          AlignedBuffer::allocate<char>(bits::nbytes(out.length), pool);
      auto raw = nulls->asMutable<uint64_t>();
      bits::fillBits(raw, 0, out.length, bits::kNull);
      holder.setBuffer(0, nulls);
    }
    return;
  }

  if (!vec.nulls()) {
    out.null_count = 0;
    return;
  }
  if (vec.encoding() == VectorEncoding::Simple::CONSTANT) {
    // If Arrow REE is used, do not need to set nulls buffer;
    // If flattenConstant is true, nulls will be set after flattening.
    out.null_count = rows.count();
    return;
  }

  auto nulls = vec.nulls();

  // If we're only exporting a subset, create a new validity buffer.
  if (rows.changed()) {
    nulls = AlignedBuffer::allocate<bool>(out.length, pool);
    gatherFromBuffer(*BOOLEAN(), *vec.nulls(), rows, options, *nulls);
  }

  // Set null counts.
  out.null_count = BaseVector::countNulls(nulls, rows.count());
  if (out.null_count > 0) {
    holder.setBuffer(0, nulls);
  }
}

bool isFlatScalarZeroCopy(const TypePtr& type) {
  // - Short decimals need to be converted to 128 bit values as they are