RNTupleUtil.hxx

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/// \file ROOT/RNTupleUtil.hxx
/// \ingroup NTuple ROOT7
/// \author Jakob Blomer <jblomer@cern.ch>
/// \date 2018-10-04
/// \warning This is part of the ROOT 7 prototype! It will change without notice. It might trigger earthquakes. Feedback
/// is welcome!

/*************************************************************************
 * Copyright (C) 1995-2019, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/

#ifndef ROOT7_RNTupleUtil
#define ROOT7_RNTupleUtil

#include <cstdint>

#include <string>
#include <vector>

namespace ROOT {
namespace Experimental {


/**
 * The fields in the ntuple model tree can carry different structural information about the type system.
 * Leaf fields contain just data, collection fields resolve to offset columns, record root fields have no
 * materialization on the primitive column layer.
 */
enum ENTupleStructure {
  kLeaf,
  kCollection,
  kRecord,
  kVariant,
  // unimplemented so far
  kReference,
};

/// Integer type long enough to hold the maximum number of entries in a column
using NTupleSize_t = std::uint64_t;
constexpr NTupleSize_t kInvalidNTupleIndex = std::uint64_t(-1);
/// Wrap the 32bit integer in a struct in order to avoid template specialization clash with std::uint32_t
struct RClusterSize {
   using ValueType = std::uint32_t;

   RClusterSize() : fValue(0) {}
   explicit constexpr RClusterSize(ValueType value) : fValue(value) {}
   RClusterSize& operator =(const ValueType value) { fValue = value; return *this; }
   RClusterSize& operator +=(const ValueType value) { fValue += value; return *this; }
   RClusterSize operator++(int) { auto result = *this; fValue++; return result; }
   operator ValueType() const { return fValue; }

   ValueType fValue;
};
using ClusterSize_t = RClusterSize;
constexpr ClusterSize_t kInvalidClusterIndex(std::uint32_t(-1));

/// Holds the index and the tag of a kSwitch column
class RColumnSwitch {
private:
   ClusterSize_t fIndex;
   std::uint32_t fTag = 0;

public:
   RColumnSwitch() = default;
   RColumnSwitch(ClusterSize_t index, std::uint32_t tag) : fIndex(index), fTag(tag) { }
   ClusterSize_t GetIndex() const { return fIndex; }
   std::uint32_t GetTag() const { return fTag; }
};

/// Uniquely identifies a physical column within the scope of the current process, used to tag pages
using ColumnId_t = std::int64_t;
constexpr ColumnId_t kInvalidColumnId = -1;

/// Distriniguishes elements of the same type within a descriptor, e.g. different fields
using DescriptorId_t = std::uint64_t;
constexpr DescriptorId_t kInvalidDescriptorId = std::uint64_t(-1);

/// Addresses a column element or field item relative to a particular cluster, instead of a global NTupleSize_t index
class RClusterIndex {
private:
   DescriptorId_t fClusterId = kInvalidDescriptorId;
   ClusterSize_t::ValueType fIndex = kInvalidClusterIndex;
public:
   RClusterIndex() = default;
   RClusterIndex(const RClusterIndex &other) = default;
   RClusterIndex &operator =(const RClusterIndex &other) = default;
   constexpr RClusterIndex(DescriptorId_t clusterId, ClusterSize_t::ValueType index)
      : fClusterId(clusterId), fIndex(index) {}

   RClusterIndex  operator+(ClusterSize_t::ValueType off) const { return RClusterIndex(fClusterId, fIndex + off); }
   RClusterIndex  operator-(ClusterSize_t::ValueType off) const { return RClusterIndex(fClusterId, fIndex - off); }
   RClusterIndex  operator++(int) /* postfix */        { auto r = *this; fIndex++; return r; }
   RClusterIndex& operator++()    /* prefix */         { ++fIndex; return *this; }
   bool operator==(const RClusterIndex &other) const {
      return fClusterId == other.fClusterId && fIndex == other.fIndex;
   }
   bool operator!=(const RClusterIndex &other) const { return !(*this == other); }

   DescriptorId_t GetClusterId() const { return fClusterId; }
   ClusterSize_t::ValueType GetIndex() const { return fIndex; }
};

/// Every NTuple is identified by a UUID.  TODO(jblomer): should this be a TUUID?
using RNTupleUuid = std::string;


/// 64 possible flags to apply to all versioned entities (so far unused).
using NTupleFlags_t = std::uint64_t;
/// For forward and backward compatibility, attach version information to
/// the consitituents of the file format (column, field, cluster, ntuple).
class RNTupleVersion {
private:
   /// The version used to write an entity
   std::uint32_t fVersionUse = 0;
   /// The minimum required version necessary to read an entity
   std::uint32_t fVersionMin = 0;
   NTupleFlags_t fFlags = 0;

public:
   RNTupleVersion() = default;
   RNTupleVersion(std::uint32_t versionUse, std::uint32_t versionMin)
     : fVersionUse(versionUse), fVersionMin(versionMin)
   {}
   RNTupleVersion(std::uint32_t versionUse, std::uint32_t versionMin, NTupleFlags_t flags)
     : fVersionUse(versionUse), fVersionMin(versionMin), fFlags(flags)
   {}

   bool operator ==(const RNTupleVersion &other) const {
      return fVersionUse == other.fVersionUse && fVersionMin == other.fVersionMin && fFlags == other.fFlags;
   }

   std::uint32_t GetVersionUse() const { return fVersionUse; }
   std::uint32_t GetVersionMin() const { return fVersionMin; }
   NTupleFlags_t GetFlags() const { return fFlags; }
};

} // namespace Experimental
} // namespace ROOT

#endif