Support streaming conformer CTC models from wenet (#427)

sherpa-onnx/csrc/online-ctc-greedy-search-decoder.cc

@@ -0,0 +1,60 @@
+// sherpa-onnx/csrc/online-ctc-greedy-search-decoder.cc
+//
+// Copyright (c)  2023  Xiaomi Corporation
+
+#include "sherpa-onnx/csrc/online-ctc-greedy-search-decoder.h"
+
+#include <algorithm>
+#include <utility>
+#include <vector>
+
+#include "sherpa-onnx/csrc/macros.h"
+
+namespace sherpa_onnx {
+
+void OnlineCtcGreedySearchDecoder::Decode(
+    Ort::Value log_probs, std::vector<OnlineCtcDecoderResult> *results) {
+  std::vector<int64_t> log_probs_shape =
+      log_probs.GetTensorTypeAndShapeInfo().GetShape();
+
+  if (log_probs_shape[0] != results->size()) {
+    SHERPA_ONNX_LOGE("Size mismatch! log_probs.size(0) %d, results.size(0): %d",
+                     static_cast<int32_t>(log_probs_shape[0]),
+                     static_cast<int32_t>(results->size()));
+    exit(-1);
+  }
+
+  int32_t batch_size = static_cast<int32_t>(log_probs_shape[0]);
+  int32_t num_frames = static_cast<int32_t>(log_probs_shape[1]);
+  int32_t vocab_size = static_cast<int32_t>(log_probs_shape[2]);
+
+  const float *p = log_probs.GetTensorData<float>();
+
+  for (int32_t b = 0; b != batch_size; ++b) {
+    auto &r = (*results)[b];
+
+    int32_t prev_id = -1;
+
+    for (int32_t t = 0; t != num_frames; ++t, p += vocab_size) {
+      int32_t y = static_cast<int32_t>(std::distance(
+          static_cast<const float *>(p),
+          std::max_element(static_cast<const float *>(p),
+                           static_cast<const float *>(p) + vocab_size)));
+
+      if (y == blank_id_) {
+        r.num_trailing_blanks += 1;
+      } else {
+        r.num_trailing_blanks = 0;
+      }
+
+      if (y != blank_id_ && y != prev_id) {
+        r.tokens.push_back(y);
+        r.timestamps.push_back(t);
+      }
+
+      prev_id = y;
+    }  // for (int32_t t = 0; t != num_frames; ++t) {
+  }    // for (int32_t b = 0; b != batch_size; ++b)
+}
+
+}  // namespace sherpa_onnx