Add PackPaddedSequence (#85)

sherpa-onnx/csrc/packed-sequence.h

@@ -0,0 +1,33 @@
+// sherpa-onnx/csrc/packed-sequence.h
+//
+// Copyright (c)  2023  Xiaomi Corporation
+#ifndef SHERPA_ONNX_CSRC_PACKED_SEQUENCE_H_
+#define SHERPA_ONNX_CSRC_PACKED_SEQUENCE_H_
+
+#include <vector>
+
+#include "onnxruntime_cxx_api.h"  // NOLINT
+
+namespace sherpa_onnx {
+
+struct PackedSequence {
+  std::vector<int32_t> sorted_indexes;
+  std::vector<int32_t> batch_sizes;
+  Ort::Value data{nullptr};
+};
+
+/** Similar to torch.nn.utils.rnn.pad_sequence but it supports only
+ * batch_first=true.
+ *
+ * @param allocator
+ * @param value  A 3-D tensor of shape (B, T, C). Its dtype is float.
+ * @param length A 1-D tensor of shape (B,). Its dtype is int64_t. Each
+ *               element in it specifies the valid length of the corresponding
+ *               entry in value before padding.
+ */
+PackedSequence PackPaddedSequence(OrtAllocator *allocator,
+                                  const Ort::Value *value, Ort::Value *length);
+
+}  // namespace sherpa_onnx
+
+#endif  // SHERPA_ONNX_CSRC_PACKED_SEQUENCE_H_