[GitHub] [arrow] JabariBooker commented on a change in pull request #12460: ARROW-13530: [C++] Implement cumulative sum compute function

[GitBox <gi...@apache.org>]

JabariBooker commented on a change in pull request #12460:
URL: https://github.com/apache/arrow/pull/12460#discussion_r819027668



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File path: cpp/src/arrow/compute/kernels/scalar_cumulative_sum.cc
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@@ -0,0 +1,147 @@
+// 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/array/array_base.h"
+#include "arrow/compute/kernels/common.h"
+#include "arrow/result.h"
+#include "arrow/visit_type_inline.h"
+
+namespace arrow {
+namespace compute {
+namespace internal {
+namespace {
+
+template <typename CType>
+CType CumulativeSum(std::shared_ptr<Array>& input, ArrayData* output, CType start) {
+  CType sum = start;
+  CType* data = checked_cast<CType*>(input->data()->buffers[1]->data());
+  CType* out_values = checked_cast<CType*>(output->buffers[1]->mutable_data());
+  for (size_t i = input->offset; i < input->length; ++i) {
+    if (input->IsValid(i)) {
+      sum += data[i];
+      out_values[i] = sum;
+    }
+  }
+
+  return sum;
+}
+
+template <typename Type>
+struct CumulativeSumFunctor {
+  using CType = TypeTraits<Type>::CType;
+
+  Status Exec(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
+    const NumericScalar& start_scalar =
+        checked_cast<const NumericScalar&>(*batch[1].scalar());
+    CType start = start_scalar.value;
+
+    switch (batch[0].kind()) {
+      case Datum::ARRAY:
+        std::shared_ptr<Array> input = batch[0].make_array();
+        ArrayData* output = out->array().get();
+
+        output->length = input->data()->length;
+        *output->type = std::move(input->type());
+        uint8_t* out_bitmap = output->buffers[0]->mutable_data();

Review comment:
       Should `mutable_address()` or `address()` be used instead as to access the buffer regardless of device? Is there an instance in which the output would be immutable?




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