[GitHub] [arrow] cyb70289 commented on a change in pull request #7418: ARROW-9115: [C++] Implementation of ascii_lower/ascii_upper by processing input data buffers in batch

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

cyb70289 commented on a change in pull request #7418:
URL: https://github.com/apache/arrow/pull/7418#discussion_r439448175



##########
File path: cpp/src/arrow/compute/kernels/scalar_string.cc
##########
@@ -37,26 +39,108 @@ struct AsciiLength {
   }
 };
 
-struct AsciiUpper {
-  // XXX: the Scalar codegen path passes template arguments that are unused
-  template <typename... Ignored>
-  static std::string Call(KernelContext*, const util::string_view& val) {
-    std::string result = val.to_string();
-    std::transform(result.begin(), result.end(), result.begin(),
-                   [](unsigned char c) { return std::toupper(c); });
-    return result;
+using TransformFunc = std::function<void(const uint8_t*, int64_t, uint8_t*)>;
+
+void StringDataTransform(KernelContext* ctx, const ExecBatch& batch,
+                         TransformFunc transform, Datum* out) {
+  if (batch[0].kind() == Datum::ARRAY) {
+    const ArrayData& input = *batch[0].array();
+    ArrayData* out_arr = out->mutable_array();
+    // Reuse offsets from input
+    out_arr->buffers[1] = input.buffers[1];

Review comment:
       These buffers[1], buffers[2] are mysterious to me. Any hint to figure it out? Thanks.




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