Add transducer modified_beam_search for RKNN. (#1949)

sherpa-onnx/csrc/rknn/online-transducer-modified-beam-search-decoder-rknn.h

@@ -0,0 +1,42 @@
+// sherpa-onnx/csrc/rknn/online-transducer-modified-beam-search-decoder-rknn.h
+//
+// Copyright (c)  2025  Xiaomi Corporation
+
+#ifndef SHERPA_ONNX_CSRC_RKNN_ONLINE_TRANSDUCER_MODIFIED_BEAM_SEARCH_DECODER_RKNN_H_
+#define SHERPA_ONNX_CSRC_RKNN_ONLINE_TRANSDUCER_MODIFIED_BEAM_SEARCH_DECODER_RKNN_H_
+
+#include <vector>
+
+#include "sherpa-onnx/csrc/rknn/online-transducer-decoder-rknn.h"
+#include "sherpa-onnx/csrc/rknn/online-zipformer-transducer-model-rknn.h"
+
+namespace sherpa_onnx {
+
+class OnlineTransducerModifiedBeamSearchDecoderRknn
+    : public OnlineTransducerDecoderRknn {
+ public:
+  explicit OnlineTransducerModifiedBeamSearchDecoderRknn(
+      OnlineZipformerTransducerModelRknn *model, int32_t max_active_paths,
+      int32_t unk_id = 2, float blank_penalty = 0.0)
+      : model_(model),
+        max_active_paths_(max_active_paths),
+        unk_id_(unk_id),
+        blank_penalty_(blank_penalty) {}
+
+  OnlineTransducerDecoderResultRknn GetEmptyResult() const override;
+
+  void StripLeadingBlanks(OnlineTransducerDecoderResultRknn *r) const override;
+
+  void Decode(std::vector<float> encoder_out,
+              OnlineTransducerDecoderResultRknn *result) const override;
+
+ private:
+  OnlineZipformerTransducerModelRknn *model_;  // Not owned
+  int32_t max_active_paths_;
+  int32_t unk_id_;
+  float blank_penalty_;
+};
+
+}  // namespace sherpa_onnx
+
+#endif  // SHERPA_ONNX_CSRC_RKNN_ONLINE_TRANSDUCER_MODIFIED_BEAM_SEARCH_DECODER_RKNN_H_