[GitHub] [arrow] felipecrv commented on a diff in pull request #34550: GH-32338: [C++] Add IPC support for Run-End Encoded Arrays

["felipecrv (via GitHub)" <gi...@apache.org>]

felipecrv commented on code in PR #34550:
URL: https://github.com/apache/arrow/pull/34550#discussion_r1136389111


##########
cpp/src/arrow/array/array_run_end.cc:
##########
@@ -85,6 +86,53 @@ void RunEndEncodedArray::SetData(const std::shared_ptr<ArrayData>& data) {
   values_array_ = MakeArray(this->data()->child_data[1]);
 }
 
+namespace {
+
+template <typename RunEndType>
+Result<std::shared_ptr<Array>> MakeLogicalRunEnds(const RunEndEncodedArray& self,
+                                                  int64_t physical_offset,
+                                                  int64_t physical_length) {
+  using RunEndCType = typename RunEndType::c_type;
+  const auto* run_ends = self.data()->child_data[0]->GetValues<RunEndCType>(1);
+  NumericBuilder<RunEndType> builder;
+  RETURN_NOT_OK(builder.Resize(physical_length));
+  if (physical_length > 0) {
+    for (int64_t i = 0; i < physical_length - 1; i++) {
+      const auto run_end = run_ends[physical_offset + i] - self.offset();
+      DCHECK_LT(run_end, self.length());
+      RETURN_NOT_OK(builder.Append(static_cast<RunEndCType>(run_end)));
+    }
+    DCHECK_GE(run_ends[physical_offset + physical_length - 1] - self.offset(),
+              self.length());
+    RETURN_NOT_OK(builder.Append(static_cast<RunEndCType>(self.length())));
+  }
+  return builder.Finish();
+}
+
+}  // namespace
+
+Result<std::shared_ptr<Array>> RunEndEncodedArray::LogicalRunEnds() const {
+  int64_t physical_offset = FindPhysicalOffset();
+  int64_t physical_length = FindPhysicalLength();
+  DCHECK(data()->child_data[0]->buffers[1]->is_cpu());
+
+  switch (run_ends_array_->type_id()) {
+    case Type::INT16:
+      return MakeLogicalRunEnds<Int16Type>(*this, physical_offset, physical_length);
+    case Type::INT32:
+      return MakeLogicalRunEnds<Int32Type>(*this, physical_offset, physical_length);
+    default:
+      break;
+  }
+  return MakeLogicalRunEnds<Int64Type>(*this, physical_offset, physical_length);

Review Comment:
   In other projects, I've been annoyed by MSVC complaining the function doesn't return a value when all the returns were in the `switch`, but I can change it here if Arrows MSVC warnings aren't so aggressive.



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