felipecrv commented on code in PR #48171:
URL: https://github.com/apache/arrow/pull/48171#discussion_r2566729261
##########
cpp/src/arrow/compute/kernels/scalar_cast_string.cc:
##########
@@ -304,8 +305,21 @@ BinaryToBinaryCastExec(KernelContext* ctx, const ExecSpan&
batch, ExecResult* ou
}
}
- // Start with a zero-copy cast, but change indices to expected size
- RETURN_NOT_OK(ZeroCopyCastExec(ctx, batch, out));
+ std::shared_ptr<ArrayData> input_arr = input.ToArrayData();
+ ArrayData* output = out->array_data().get();
+ output->length = input_arr->length;
+ output->SetNullCount(input_arr->null_count);
+ output->buffers = std::move(input_arr->buffers);
+ output->child_data = std::move(input_arr->child_data);
+
+ if (output->buffers[0]) {
+ // If reusing the null bitmap, ensure offset into the first byte is the
same as input.
+ output->offset = input_arr->offset % 8;
+ output->buffers[0] = SliceBuffer(output->buffers[0], input_arr->offset /
8);
+ } else {
+ output->offset = 0;
+ }
Review Comment:
But if you don't slice they get reallocated with the same length, no?
Nevertheless, it becomes a creates a very weird relationship between this code
and the function. Making it very non-obvious how it is correct.
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