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+++ b/mupdf-source/thirdparty/tesseract/src/lstm/parallel.h	Mon Sep 15 11:43:07 2025 +0200
@@ -0,0 +1,84 @@
+///////////////////////////////////////////////////////////////////////
+// File:        parallel.h
+// Description: Runs networks in parallel on the same input.
+// Author:      Ray Smith
+//
+// (C) Copyright 2013, Google Inc.
+// 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.
+///////////////////////////////////////////////////////////////////////
+
+#ifndef TESSERACT_LSTM_PARALLEL_H_
+#define TESSERACT_LSTM_PARALLEL_H_
+
+#include "plumbing.h"
+
+namespace tesseract {
+
+// Runs multiple networks in parallel, interlacing their outputs.
+class Parallel : public Plumbing {
+public:
+  // ni_ and no_ will be set by AddToStack.
+  TESS_API
+  Parallel(const std::string &name, NetworkType type);
+
+  // Returns the shape output from the network given an input shape (which may
+  // be partially unknown ie zero).
+  StaticShape OutputShape(const StaticShape &input_shape) const override;
+
+  std::string spec() const override {
+    std::string spec;
+    if (type_ == NT_PAR_2D_LSTM) {
+      // We have 4 LSTMs operating in parallel here, so the size of each is
+      // the number of outputs/4.
+      spec += "L2xy" + std::to_string(no_ / 4);
+    } else if (type_ == NT_PAR_RL_LSTM) {
+      // We have 2 LSTMs operating in parallel here, so the size of each is
+      // the number of outputs/2.
+      if (stack_[0]->type() == NT_LSTM_SUMMARY) {
+        spec += "Lbxs" + std::to_string(no_ / 2);
+      } else {
+        spec += "Lbx" + std::to_string(no_ / 2);
+      }
+    } else {
+      if (type_ == NT_REPLICATED) {
+        spec += "R" + std::to_string(stack_.size()) + "(" + stack_[0]->spec();
+      } else {
+        for (auto &it : stack_) {
+          spec += it->spec();
+        }
+      }
+      spec += ")";
+    }
+    return spec;
+  }
+
+  // Runs forward propagation of activations on the input line.
+  // See Network for a detailed discussion of the arguments.
+  void Forward(bool debug, const NetworkIO &input, const TransposedArray *input_transpose,
+               NetworkScratch *scratch, NetworkIO *output) override;
+
+  // Runs backward propagation of errors on the deltas line.
+  // See Network for a detailed discussion of the arguments.
+  bool Backward(bool debug, const NetworkIO &fwd_deltas, NetworkScratch *scratch,
+                NetworkIO *back_deltas) override;
+
+private:
+  // If *this is a NT_REPLICATED, then it feeds a replicated network with
+  // identical inputs, and it would be extremely wasteful for them to each
+  // calculate and store the same transpose of the inputs, so Parallel does it
+  // and passes a pointer to the replicated network, allowing it to use the
+  // transpose on the next call to Backward.
+  TransposedArray transposed_input_;
+};
+
+} // namespace tesseract.
+
+#endif // TESSERACT_LSTM_PARALLEL_H_