TAxis.cxx

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/// \file TAxis.cxx
/// \ingroup Hist ROOT7
/// \author Axel Naumann <axel@cern.ch>
/// \date 2015-08-06
/// \warning This is part of the ROOT 7 prototype! It will change without notice. It might trigger earthquakes. Feedback is welcome!

/*************************************************************************
 * Copyright (C) 1995-2015, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/

#include "ROOT/TAxis.h"

#include <cmath>

constexpr const int ROOT::TAxisBase::kNOverflowBins[4];

/// If the coordinate `x` is a bin low edge (within 1E-6 of the coordinate),
/// return the bin for which this is a low edge. If it's not a bin edge, return
/// -1.
int ROOT::TAxisEquidistant::GetBinIndexForLowEdge(double x) const noexcept {
  // fracBinIdx is the fractional bin index of x in this axis. It's (close to)
  // an integer if it's an axis border.
  double fracBinIdx = (x - GetMinimum()) * fInvBinWidth;
  // fracBinIdx might be 12.99999999. It's a bin border if the deviation from
  // an actual bin border is "fairly small".
  int binIdx = std::round(fracBinIdx + 0.5);
  double binOffset = fracBinIdx - binIdx;
  if (std::fabs(binOffset) > x * 1E-6)
    return -1;

  // If the bin index is below the first bin (i.e. x is the lower edge of the
  // underflow bin) then it's out of range.
  if (IsUnderflowBin(binIdx))
    return -1;
  // If x is the lower edge of the overflow bin then that's still okay - but if
  // even the bin before binIdx is an overflow it's out of range.
  if (IsOverflowBin(binIdx - 1))
    return -1;

  return binIdx;
}

/// Whether (and how) the source axis can be merged into the target axis.
ROOT::EAxisCompatibility
ROOT::CanMap(TAxisEquidistant& target, TAxisEquidistant& source) noexcept {
  if (source == target)
    return EAxisCompatibility::kIdentical;

  int idxTargetLow = target.GetBinIndexForLowEdge(source.GetMinimum());
  int idxTargetHigh = target.GetBinIndexForLowEdge(source.GetMaximum());
  if (idxTargetLow < 0 || idxTargetHigh < 0)
    return EAxisCompatibility::kIncompatible;

  // If both low and high exist in both axes and the bin width is identical then
  // one axis contains the other.
  if (source.GetInverseBinWidth() == target.GetInverseBinWidth())
    return EAxisCompatibility::kContains;

  // Now we are left with the case
  //   source: 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6
  //   target: ...0.0, 0.3, 0.6...
  // The question is: is the ratio of the bin width identical to the ratio of
  // the number of bin?
  if (std::fabs(target.GetInverseBinWidth() * source.GetNBinsNoOver()
                - source.GetInverseBinWidth() * (idxTargetHigh - idxTargetLow))
      > 1E-6 * target.GetInverseBinWidth())
    return EAxisCompatibility::kIncompatible;

  // source is a fine-grained version of target.
  return EAxisCompatibility::kSampling;
}

//TODO: the other CanMap() overloads