PayLoadSG.h

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// Copyright 2019-2020 CERN and copyright holders of ALICE O2.
// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
// All rights not expressly granted are reserved.
//
// This software is distributed under the terms of the GNU General Public
// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
//
// In applying this license CERN does not waive the privileges and immunities
// granted to it by virtue of its status as an Intergovernmental Organization
// or submit itself to any jurisdiction.
 
#ifndef ALICEO2_ITSMFT_PAYLOADSG_H
#define ALICEO2_ITSMFT_PAYLOADSG_H
 
#include <cstdint>
#include <vector>
#include <Rtypes.h>
 
 
namespace o2
{
namespace itsmft
{
 
class PayLoadSG
{
  // scatter-gather buffer for the payload: base pointer + vector of references for pieces to collect
 public:
  using DataType = unsigned char;
 
  PayLoadSG() = default;
  ~PayLoadSG() = default;
 
  void add(const DataType* ptr, size_t n)
  {
    if (n) {
      mBuffer.emplace_back(ptr, n);
    }
  }
 
  bool current(char& v)
  {
    if (mCurrentPieceID < mBuffer.size()) {
      const auto& piece = mBuffer[mCurrentPieceID];
      if (mCurrentEntryInPiece < piece.size) {
        v = piece.data[mCurrentEntryInPiece];
        return true;
      } else {
        nextPiece();
        return current(v);
      }
    }
    return false;
  }
 
  bool next(char& v)
  {
    if (mCurrentPieceID < mBuffer.size()) {
      const auto& piece = mBuffer[mCurrentPieceID];
      if (mCurrentEntryInPiece < piece.size) {
        v = piece.data[mCurrentEntryInPiece++];
        return true;
      } else {
        nextPiece();
        return next(v);
      }
    }
    return false;
  }
 
  bool next(uint16_t& v)
  {
    char b0, b1;
    if (next(b0) && next(b1)) {
      v = (b0 << 8) | b1;
      return true;
    }
    return false;
  }
 
  void rewind()
  {
    mCurrentPieceID = mCurrentEntryInPiece = 0;
  }
 
  void clear()
  {
    mBuffer.clear();
    mCurrentPieceID = mCurrentEntryInPiece = 0;
  }
 
  struct SGPiece {
    const DataType* data = nullptr; // data of the piece
    uint32_t size = 0;              // size of the piece
    SGPiece() = default;
    SGPiece(const DataType* st, int n) : data(st), size(n) {}
  };
 
  void setDone() { mCurrentPieceID = mBuffer.size(); }
 
  size_t& currentPieceID() { return mCurrentPieceID; }
  size_t currentPieceID() const { return mCurrentPieceID; }
 
  size_t& currentEntryInPiece() { return mCurrentEntryInPiece; }
  size_t currentEntryInPiece() const { return mCurrentEntryInPiece; }
 
  const SGPiece* currentPiece() const { return mCurrentPieceID < mBuffer.size() ? &mBuffer[mCurrentPieceID] : nullptr; }
 
  const SGPiece* nextPiece()
  {
    // move to the next piece
    mCurrentEntryInPiece = 0;
    mCurrentPieceID++;
    return currentPiece();
  }
 
  const SGPiece* getPiece(int i) const { return &mBuffer[i]; }
 
  size_t getNPieces() const { return mBuffer.size(); }
 
 private:
  std::vector<SGPiece> mBuffer;   // list of pieces to fetch
  size_t mCurrentPieceID = 0;     // current piece
  size_t mCurrentEntryInPiece = 0; // offset within current piece
 
  ClassDefNV(PayLoadSG, 1);
};
} // namespace itsmft
} // namespace o2
 
#endif