bit-stream-utils.h

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// Copyright 2012 Cloudera Inc.
//
// 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.


#ifndef IMPALA_UTIL_BIT_STREAM_UTILS_H
#define IMPALA_UTIL_BIT_STREAM_UTILS_H

#include <boost/cstdint.hpp>
#include <string.h>
#include "common/compiler-util.h"
#include "common/logging.h"
#include "util/bit-util.h"

namespace impala {

class BitWriter {
 public:
  BitWriter(uint8_t* buffer, int buffer_len) :
      buffer_(buffer),
      max_bytes_(buffer_len) {
    Clear();
  }

  void Clear() {
    buffered_values_ = 0;
    byte_offset_ = 0;
    bit_offset_ = 0;
  }

  int bytes_written() const { return byte_offset_ + BitUtil::Ceil(bit_offset_, 8); }
  uint8_t* buffer() const { return buffer_; }
  int buffer_len() const { return max_bytes_; }

  bool PutValue(uint64_t v, int num_bits);

  template<typename T>
  bool PutAligned(T v, int num_bytes);

  bool PutVlqInt(int32_t v);

  uint8_t* GetNextBytePtr(int num_bytes = 1);

  void Flush(bool align=false);

 private:
  uint8_t* buffer_;
  int max_bytes_;

  uint64_t buffered_values_;

  int byte_offset_;       // Offset in buffer_
  int bit_offset_;        // Offset in buffered_values_
};

class BitReader {
 public:
  BitReader(uint8_t* buffer, int buffer_len) :
      buffer_(buffer),
      max_bytes_(buffer_len),
      byte_offset_(0),
      bit_offset_(0) {
    int num_bytes = std::min(8, max_bytes_ - byte_offset_);
    memcpy(&buffered_values_, buffer_ + byte_offset_, num_bytes);
  }

  BitReader() : buffer_(NULL), max_bytes_(0) {}

  template<typename T>
  bool GetValue(int num_bits, T* v);

  template<typename T>
  bool GetAligned(int num_bytes, T* v);

  bool GetVlqInt(int32_t* v);

  int bytes_left() { return max_bytes_ - (byte_offset_ + BitUtil::Ceil(bit_offset_, 8)); }

  static const int MAX_VLQ_BYTE_LEN = 5;

 private:
  uint8_t* buffer_;
  int max_bytes_;

  uint64_t buffered_values_;

  int byte_offset_;       // Offset in buffer_
  int bit_offset_;        // Offset in buffered_values_
};

}

#endif