add pad_sequence (#84)

sherpa-onnx/csrc/pad-sequence.h

@@ -0,0 +1,31 @@
+// sherpa-onnx/csrc/pad-sequence.h
+//
+// Copyright (c)  2023  Xiaomi Corporation
+#ifndef SHERPA_ONNX_CSRC_PAD_SEQUENCE_H_
+#define SHERPA_ONNX_CSRC_PAD_SEQUENCE_H_
+
+#include <vector>
+
+#include "onnxruntime_cxx_api.h"  // NOLINT
+
+namespace sherpa_onnx {
+
+/** Similar to torch.nn.utils.rnn.pad_sequence but it supports only
+ * batch_first=true.
+ *
+ * @param allocator
+ * @param values A list of 2-D tensors. Each tensor's second dimension
+ *               must be the same and the data type of each tensor should
+ *               be float.
+ * @param padding_value Value used for padding. For log-fbank, you usually use
+ *                      -23.025850929940457f as the padding value.
+ *
+ * @return Return a 3-D tensor of shape (B, max_T, C).
+ */
+Ort::Value PadSequence(OrtAllocator *allocator,
+                       const std::vector<const Ort::Value *> &values,
+                       float padding_value);
+
+}  // namespace sherpa_onnx
+
+#endif  // SHERPA_ONNX_CSRC_PAD_SEQUENCE_H_