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diff --git a/extern/draco/draco/src/draco/compression/bit_coders/adaptive_rans_bit_decoder.h b/extern/draco/draco/src/draco/compression/bit_coders/adaptive_rans_bit_decoder.h
new file mode 100644
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+++ b/extern/draco/draco/src/draco/compression/bit_coders/adaptive_rans_bit_decoder.h
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+// Copyright 2016 The Draco Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// File provides basic classes and functions for rANS bit decoding.
+#ifndef DRACO_COMPRESSION_BIT_CODERS_ADAPTIVE_RANS_BIT_DECODER_H_
+#define DRACO_COMPRESSION_BIT_CODERS_ADAPTIVE_RANS_BIT_DECODER_H_
+
+#include <vector>
+
+#include "draco/compression/entropy/ans.h"
+#include "draco/core/decoder_buffer.h"
+
+namespace draco {
+
+// Class for decoding a sequence of bits that were encoded with
+// AdaptiveRAnsBitEncoder.
+class AdaptiveRAnsBitDecoder {
+ public:
+  AdaptiveRAnsBitDecoder();
+  ~AdaptiveRAnsBitDecoder();
+
+  // Sets |source_buffer| as the buffer to decode bits from.
+  bool StartDecoding(DecoderBuffer *source_buffer);
+
+  // Decode one bit. Returns true if the bit is a 1, otherwise false.
+  bool DecodeNextBit();
+
+  // Decode the next |nbits| and return the sequence in |value|. |nbits| must be
+  // > 0 and <= 32.
+  void DecodeLeastSignificantBits32(int nbits, uint32_t *value);
+
+  void EndDecoding() {}
+
+ private:
+  void Clear();
+
+  AnsDecoder ans_decoder_;
+  double p0_f_;
+};
+
+}  // namespace draco
+
+#endif  // DRACO_COMPRESSION_BIT_CODERS_ADAPTIVE_RANS_BIT_DECODER_H_