[GitHub] [arrow] zeroshade commented on a diff in pull request #34195: GH-32105: [C++] Encode and decode Run-End Encoded vectors

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

zeroshade commented on code in PR #34195:
URL: https://github.com/apache/arrow/pull/34195#discussion_r1119382712


##########
cpp/src/arrow/compute/kernels/vector_run_end_encode.cc:
##########
@@ -0,0 +1,652 @@
+// 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 <utility>
+
+#include "arrow/compute/api_vector.h"
+#include "arrow/compute/kernels/common_internal.h"
+#include "arrow/util/checked_cast.h"
+#include "arrow/util/ree_util.h"
+
+namespace arrow {
+namespace compute {
+namespace internal {
+
+template <typename ArrowType, bool has_validity_buffer>
+struct ReadValueImpl {
+  using CType = typename ArrowType::c_type;
+
+  [[nodiscard]] bool ReadValue(const uint8_t* input_validity, const void* input_values,
+                               CType* out, int64_t read_offset) const {
+    bool valid = true;
+    if constexpr (has_validity_buffer) {
+      valid = bit_util::GetBit(input_validity, read_offset);
+    }
+    if (valid) {
+      *out = (reinterpret_cast<const CType*>(input_values))[read_offset];
+    }
+    return valid;
+  }
+};
+
+template <>
+bool ReadValueImpl<BooleanType, true>::ReadValue(const uint8_t* input_validity,
+                                                 const void* input_values, CType* out,
+                                                 int64_t read_offset) const {
+  const bool valid = bit_util::GetBit(input_validity, read_offset);
+  *out = valid &&
+         bit_util::GetBit(reinterpret_cast<const uint8_t*>(input_values), read_offset);
+  return valid;
+}
+
+template <>
+bool ReadValueImpl<BooleanType, false>::ReadValue(const uint8_t* input_validity,
+                                                  const void* input_values, CType* out,
+                                                  int64_t read_offset) const {
+  *out = bit_util::GetBit(reinterpret_cast<const uint8_t*>(input_values), read_offset);
+  return true;
+}
+

Review Comment:
   Shouldn't we need another explicit implementation here for handling variable and fixed length binary arrays? I don't see anything elsewhere for handling encoding/decoding of that type.



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