Add RNN LM rescore for offline ASR with modified_beam_search (#125)

sherpa-onnx/csrc/offline-lm-config.h

@@ -0,0 +1,33 @@
+// sherpa-onnx/csrc/offline-lm-config.h
+//
+// Copyright (c)  2023  Xiaomi Corporation
+#ifndef SHERPA_ONNX_CSRC_OFFLINE_LM_CONFIG_H_
+#define SHERPA_ONNX_CSRC_OFFLINE_LM_CONFIG_H_
+
+#include <string>
+
+#include "sherpa-onnx/csrc/parse-options.h"
+
+namespace sherpa_onnx {
+
+struct OfflineLMConfig {
+  // path to the onnx model
+  std::string model;
+
+  // LM scale
+  float scale = 1.0;
+
+  OfflineLMConfig() = default;
+
+  OfflineLMConfig(const std::string &model, float scale)
+      : model(model), scale(scale) {}
+
+  void Register(ParseOptions *po);
+  bool Validate() const;
+
+  std::string ToString() const;
+};
+
+}  // namespace sherpa_onnx
+
+#endif  // SHERPA_ONNX_CSRC_OFFLINE_LM_CONFIG_H_