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diff --git a/extern/draco/draco/src/draco/compression/attributes/prediction_schemes/mesh_prediction_scheme_parallelogram_shared.h b/extern/draco/draco/src/draco/compression/attributes/prediction_schemes/mesh_prediction_scheme_parallelogram_shared.h
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+++ b/extern/draco/draco/src/draco/compression/attributes/prediction_schemes/mesh_prediction_scheme_parallelogram_shared.h
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+// Copyright 2016 The Draco Authors.
+//
+// Licensed 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.
+//
+// Shared functionality for different parallelogram prediction schemes.
+
+#ifndef DRACO_COMPRESSION_ATTRIBUTES_PREDICTION_SCHEMES_MESH_PREDICTION_SCHEME_PARALLELOGRAM_SHARED_H_
+#define DRACO_COMPRESSION_ATTRIBUTES_PREDICTION_SCHEMES_MESH_PREDICTION_SCHEME_PARALLELOGRAM_SHARED_H_
+
+#include "draco/mesh/corner_table.h"
+#include "draco/mesh/mesh.h"
+
+namespace draco {
+
+// TODO(draco-eng) consolidate Vertex/next/previous queries to one call
+// (performance).
+template <class CornerTableT>
+inline void GetParallelogramEntries(
+    const CornerIndex ci, const CornerTableT *table,
+    const std::vector<int32_t> &vertex_to_data_map, int *opp_entry,
+    int *next_entry, int *prev_entry) {
+  // One vertex of the input |table| correspond to exactly one attribute value
+  // entry. The |table| can be either CornerTable for per-vertex attributes,
+  // or MeshAttributeCornerTable for attributes with interior seams.
+  *opp_entry = vertex_to_data_map[table->Vertex(ci).value()];
+  *next_entry = vertex_to_data_map[table->Vertex(table->Next(ci)).value()];
+  *prev_entry = vertex_to_data_map[table->Vertex(table->Previous(ci)).value()];
+}
+
+// Computes parallelogram prediction for a given corner and data entry id.
+// The prediction is stored in |out_prediction|.
+// Function returns false when the prediction couldn't be computed, e.g. because
+// not all entry points were available.
+template <class CornerTableT, typename DataTypeT>
+inline bool ComputeParallelogramPrediction(
+    int data_entry_id, const CornerIndex ci, const CornerTableT *table,
+    const std::vector<int32_t> &vertex_to_data_map, const DataTypeT *in_data,
+    int num_components, DataTypeT *out_prediction) {
+  const CornerIndex oci = table->Opposite(ci);
+  if (oci == kInvalidCornerIndex) {
+    return false;
+  }
+  int vert_opp, vert_next, vert_prev;
+  GetParallelogramEntries<CornerTableT>(oci, table, vertex_to_data_map,
+                                        &vert_opp, &vert_next, &vert_prev);
+  if (vert_opp < data_entry_id && vert_next < data_entry_id &&
+      vert_prev < data_entry_id) {
+    // Apply the parallelogram prediction.
+    const int v_opp_off = vert_opp * num_components;
+    const int v_next_off = vert_next * num_components;
+    const int v_prev_off = vert_prev * num_components;
+    for (int c = 0; c < num_components; ++c) {
+      out_prediction[c] = (in_data[v_next_off + c] + in_data[v_prev_off + c]) -
+                          in_data[v_opp_off + c];
+    }
+    return true;
+  }
+  return false;  // Not all data is available for prediction
+}
+
+}  // namespace draco
+
+#endif  // DRACO_COMPRESSION_ATTRIBUTES_PREDICTION_SCHEMES_MESH_PREDICTION_SCHEME_PARALLELOGRAM_SHARED_H_