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

sherpa-onnx/csrc/offline-rnn-lm.cc

@@ -0,0 +1,74 @@
+// sherpa-onnx/csrc/offline-rnn-lm.cc
+//
+// Copyright (c)  2023  Xiaomi Corporation
+
+#include "sherpa-onnx/csrc/offline-rnn-lm.h"
+
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "onnxruntime_cxx_api.h"  // NOLINT
+#include "sherpa-onnx/csrc/macros.h"
+#include "sherpa-onnx/csrc/onnx-utils.h"
+#include "sherpa-onnx/csrc/text-utils.h"
+
+namespace sherpa_onnx {
+
+class OfflineRnnLM::Impl {
+ public:
+  explicit Impl(const OfflineLMConfig &config)
+      : config_(config),
+        env_(ORT_LOGGING_LEVEL_ERROR),
+        sess_opts_{},
+        allocator_{} {
+    Init(config);
+  }
+
+  Ort::Value Rescore(Ort::Value x, Ort::Value x_lens) {
+    std::array<Ort::Value, 2> inputs = {std::move(x), std::move(x_lens)};
+
+    auto out =
+        sess_->Run({}, input_names_ptr_.data(), inputs.data(), inputs.size(),
+                   output_names_ptr_.data(), output_names_ptr_.size());
+
+    return std::move(out[0]);
+  }
+
+ private:
+  void Init(const OfflineLMConfig &config) {
+    auto buf = ReadFile(config_.model);
+
+    sess_ = std::make_unique<Ort::Session>(env_, buf.data(), buf.size(),
+                                           sess_opts_);
+
+    GetInputNames(sess_.get(), &input_names_, &input_names_ptr_);
+
+    GetOutputNames(sess_.get(), &output_names_, &output_names_ptr_);
+  }
+
+ private:
+  OfflineLMConfig config_;
+  Ort::Env env_;
+  Ort::SessionOptions sess_opts_;
+  Ort::AllocatorWithDefaultOptions allocator_;
+
+  std::unique_ptr<Ort::Session> sess_;
+
+  std::vector<std::string> input_names_;
+  std::vector<const char *> input_names_ptr_;
+
+  std::vector<std::string> output_names_;
+  std::vector<const char *> output_names_ptr_;
+};
+
+OfflineRnnLM::OfflineRnnLM(const OfflineLMConfig &config)
+    : impl_(std::make_unique<Impl>(config)) {}
+
+OfflineRnnLM::~OfflineRnnLM() = default;
+
+Ort::Value OfflineRnnLM::Rescore(Ort::Value x, Ort::Value x_lens) {
+  return impl_->Rescore(std::move(x), std::move(x_lens));
+}
+
+}  // namespace sherpa_onnx