scott-routledge2 commented on code in PR #48171:
URL: https://github.com/apache/arrow/pull/48171#discussion_r2556567561
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cpp/src/arrow/compute/kernels/scalar_cast_string.cc:
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@@ -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:
Thanks for the suggestions! I didn't slice the offset buffers originally
because they are reallocated by `CastBinaryToBinaryOffsets` with the correct
offset. Although, this would only be true for the case where the offset type
changes, in the case where the offset stays the same then we would either have
to slice here or call `ZeroCopyCastExec` like in the comment above?
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