BitStream.h

/**************************************************************************
 * basf2 (Belle II Analysis Software Framework)                           *
 * Author: The Belle II Collaboration                                     *
 *                                                                        *
 * See git log for contributors and copyright holders.                    *
 * This file is licensed under LGPL-3.0, see LICENSE.md.                  *
 **************************************************************************/
 
#pragma once
#include <vector>
#include <framework/utilities/Utils.h>
 
namespace Belle2::ECL {
 
  class BitStream {
  public:
    BitStream(): m_pos(0), m_store(1, 0) {}
 
    explicit BitStream(int n): m_pos(0), m_store(n, 0) {}
 
    void putNBits(unsigned int value, unsigned int n)
    {
      unsigned int bpos = m_pos % 32, wpos = m_pos / 32;
      value &= 0xffffffffu >> (32 - n);
// check if we have enough space and double in size if necessary.
      if (branch_unlikely(m_pos + n > m_store.size() * 32)) m_store.resize(2 * m_store.size(), 0);
      m_store[wpos] |= value << bpos;
      if (bpos + n > 32) m_store[wpos + 1] = value >> (32 - bpos);
      m_pos += n;
    }
 
    unsigned int getNBits(unsigned int n)
    {
      unsigned int bpos = m_pos % 32, wpos = m_pos / 32;
// make sure we don't access memory we don't own
      if (branch_unlikely(m_pos + n > m_store.size() * 32)) throw std::range_error("Not enough bits in stream");
      unsigned int res = m_store[wpos] >> bpos;
      if (bpos + n > 32) res |= m_store[wpos + 1] << (32 - bpos);
      m_pos += n;
      return res & (0xffffffffu >> (32 - n));
    }
 
    size_t getPos() const {return m_pos;}
 
    void setPos(size_t pos) {m_pos = pos;}
 
    std::vector<unsigned int>& getStore() {return m_store;}
 
    void resize()
    {
      m_store.resize((m_pos + 31) / 32);
    }
  protected:
    size_t m_pos; 
    std::vector<unsigned int> m_store; 
  };
}