Support Agglomerative clustering. (#1384)

We use the open-source implementation from
https://github.com/cdalitz/hclust-cpp

sherpa-onnx/csrc/fast-clustering-config.cc

@@ -0,0 +1,45 @@
+// sherpa-onnx/csrc/fast-clustering-config.cc
+//
+// Copyright (c)  2024  Xiaomi Corporation
+
+#include "sherpa-onnx/csrc/fast-clustering-config.h"
+
+#include <sstream>
+#include <string>
+
+#include "sherpa-onnx/csrc/macros.h"
+
+namespace sherpa_onnx {
+std::string FastClusteringConfig::ToString() const {
+  std::ostringstream os;
+
+  os << "FastClusteringConfig(";
+  os << "num_clusters=" << num_clusters << ", ";
+  os << "threshold=" << threshold << ")";
+
+  return os.str();
+}
+
+void FastClusteringConfig::Register(ParseOptions *po) {
+  std::string prefix = "ctc";
+  ParseOptions p(prefix, po);
+
+  p.Register("num-clusters", &num_clusters,
+             "Number of cluster. If greater than 0, then --cluster-thresold is "
+             "ignored");
+
+  p.Register("cluster-threshold", &threshold,
+             "If --num-clusters is not specified, then it specifies the "
+             "distance threshold for clustering.");
+}
+
+bool FastClusteringConfig::Validate() const {
+  if (num_clusters < 1 && threshold < 0) {
+    SHERPA_ONNX_LOGE("Please provide either num_clusters or threshold");
+    return false;
+  }
+
+  return true;
+}
+
+}  // namespace sherpa_onnx