Add CTC HLG decoding using OpenFst (#349)

sherpa-onnx/csrc/offline-ctc-fst-decoder-config.h

@@ -0,0 +1,31 @@
+// sherpa-onnx/csrc/offline-ctc-fst-decoder-config.h
+//
+// Copyright (c)  2023  Xiaomi Corporation
+
+#ifndef SHERPA_ONNX_CSRC_OFFLINE_CTC_FST_DECODER_CONFIG_H_
+#define SHERPA_ONNX_CSRC_OFFLINE_CTC_FST_DECODER_CONFIG_H_
+
+#include <string>
+
+#include "sherpa-onnx/csrc/parse-options.h"
+
+namespace sherpa_onnx {
+
+struct OfflineCtcFstDecoderConfig {
+  // Path to H.fst, HL.fst or HLG.fst
+  std::string graph;
+  int32_t max_active = 3000;
+
+  OfflineCtcFstDecoderConfig() = default;
+
+  OfflineCtcFstDecoderConfig(const std::string &graph, int32_t max_active)
+      : graph(graph), max_active(max_active) {}
+
+  std::string ToString() const;
+
+  void Register(ParseOptions *po);
+};
+
+}  // namespace sherpa_onnx
+
+#endif  // SHERPA_ONNX_CSRC_OFFLINE_CTC_FST_DECODER_CONFIG_H_