adaptive_rans_bit_encoder.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 encoding.
#ifndef DRACO_COMPRESSION_BIT_CODERS_ADAPTIVE_RANS_BIT_ENCODER_H_
#define DRACO_COMPRESSION_BIT_CODERS_ADAPTIVE_RANS_BIT_ENCODER_H_
 
#include <vector>
 
#include "draco/compression/entropy/ans.h"
#include "draco/core/encoder_buffer.h"
 
namespace draco {
 
// Class for adaptive encoding a sequence of bits using rANS.
class AdaptiveRAnsBitEncoder {
 public:
  AdaptiveRAnsBitEncoder();
  ~AdaptiveRAnsBitEncoder();
 
  // Must be called before any Encode* function is called.
  void StartEncoding();
 
  // Encode one bit. If |bit| is true encode a 1, otherwise encode a 0.
  void EncodeBit(bool bit) { bits_.push_back(bit); }
 
  // Encode |nbits| of |value|, starting from the least significant bit.
  // |nbits| must be > 0 and <= 32.
  void EncodeLeastSignificantBits32(int nbits, uint32_t value) {
    DRACO_DCHECK_EQ(true, nbits <= 32);
    DRACO_DCHECK_EQ(true, nbits > 0);
    uint32_t selector = (1 << (nbits - 1));
    while (selector) {
      EncodeBit(value & selector);
      selector = selector >> 1;
    }
  }
 
  // Ends the bit encoding and stores the result into the target_buffer.
  void EndEncoding(EncoderBuffer *target_buffer);
 
 private:
  void Clear();
 
  std::vector<bool> bits_;
};
 
}  // namespace draco
 
#endif  // DRACO_COMPRESSION_BIT_CODERS_ADAPTIVE_RANS_BIT_ENCODER_H_