Rework cudf::strings::from_booleans to use make_strings_children (#12365

)

Issue #12167
 
Use `make_strings_children` in `cudf::strings::from_booleans` to simplify code and make the function more robust.

Authors:
  - Vukasin Milovanovic (https://github.com/vuule)

Approvers:
  - David Wendt (https://github.com/davidwendt)
  - Divye Gala (https://github.com/divyegala)

URL: #12365

cpp/src/strings/convert/convert_booleans.cu

@@ -90,6 +90,32 @@ std::unique_ptr<column> to_booleans(strings_column_view const& strings,
 }
 
 namespace detail {
+
+namespace {
+struct from_booleans_fn {
+  column_device_view const d_column;
+  string_view d_true;
+  string_view d_false;
+  offset_type* d_offsets{};
+  char* d_chars{};
+
+  __device__ void operator()(size_type idx) const
+  {
+    if (d_column.is_null(idx)) {
+      if (d_chars == nullptr) d_offsets[idx] = 0;
+      return;
+    }
+
+    if (d_chars != nullptr) {
+      auto const result = d_column.element<bool>(idx) ? d_true : d_false;
+      memcpy(d_chars + d_offsets[idx], result.data(), result.size_bytes());
+    } else {
+      d_offsets[idx] = d_column.element<bool>(idx) ? d_true.size_bytes() : d_false.size_bytes();
+    }
+  };
+};
+}  // namespace
+
 // Convert boolean column to strings column
 std::unique_ptr<column> from_booleans(column_view const& booleans,
                                       string_scalar const& true_string,
@@ -113,34 +139,13 @@ std::unique_ptr<column> from_booleans(column_view const& booleans,
 
   // copy null mask
   rmm::device_buffer null_mask = cudf::detail::copy_bitmask(booleans, stream, mr);
-  // build offsets column
-  auto offsets_transformer_itr = cudf::detail::make_counting_transform_iterator(
-    0, [d_column, d_true, d_false] __device__(size_type idx) {
-      if (d_column.is_null(idx)) return 0;
-      return d_column.element<bool>(idx) ? d_true.size_bytes() : d_false.size_bytes();
-    });
-  auto offsets_column = make_offsets_child_column(
-    offsets_transformer_itr, offsets_transformer_itr + strings_count, stream, mr);
-  auto offsets_view = offsets_column->view();
-  auto d_offsets    = offsets_view.data<int32_t>();
-
-  // build chars column
-  auto const bytes =
-    cudf::detail::get_value<int32_t>(offsets_column->view(), strings_count, stream);
-  auto chars_column = create_chars_child_column(bytes, stream, mr);
-  auto d_chars      = chars_column->mutable_view().data<char>();
-  thrust::for_each_n(rmm::exec_policy(stream),
-                     thrust::make_counting_iterator<size_type>(0),
-                     strings_count,
-                     [d_column, d_true, d_false, d_offsets, d_chars] __device__(size_type idx) {
-                       if (d_column.is_null(idx)) return;
-                       string_view result = (d_column.element<bool>(idx) ? d_true : d_false);
-                       memcpy(d_chars + d_offsets[idx], result.data(), result.size_bytes());
-                     });
+
+  auto children =
+    make_strings_children(from_booleans_fn{d_column, d_true, d_false}, strings_count, stream, mr);
 
   return make_strings_column(strings_count,
-                             std::move(offsets_column),
-                             std::move(chars_column),
+                             std::move(children.first),
+                             std::move(children.second),
                              booleans.null_count(),
                              std::move(null_mask));
 }