Add HLG decoding for streaming CTC models (#731)

sherpa-onnx/csrc/online-ctc-fst-decoder-config.cc

@@ -0,0 +1,40 @@
+// sherpa-onnx/csrc/online-ctc-fst-decoder-config.cc
+//
+// Copyright (c)  2024  Xiaomi Corporation
+
+#include "sherpa-onnx/csrc/online-ctc-fst-decoder-config.h"
+
+#include <sstream>
+#include <string>
+
+#include "sherpa-onnx/csrc/file-utils.h"
+#include "sherpa-onnx/csrc/macros.h"
+
+namespace sherpa_onnx {
+
+std::string OnlineCtcFstDecoderConfig::ToString() const {
+  std::ostringstream os;
+
+  os << "OnlineCtcFstDecoderConfig(";
+  os << "graph=\"" << graph << "\", ";
+  os << "max_active=" << max_active << ")";
+
+  return os.str();
+}
+
+void OnlineCtcFstDecoderConfig::Register(ParseOptions *po) {
+  po->Register("ctc-graph", &graph, "Path to H.fst, HL.fst, or HLG.fst");
+
+  po->Register("ctc-max-active", &max_active,
+               "Decoder max active states.  Larger->slower; more accurate");
+}
+
+bool OnlineCtcFstDecoderConfig::Validate() const {
+  if (!graph.empty() && !FileExists(graph)) {
+    SHERPA_ONNX_LOGE("graph: %s does not exist", graph.c_str());
+    return false;
+  }
+  return true;
+}
+
+}  // namespace sherpa_onnx