Integer overflow in TTree::Draw

[vepadulano]

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Description

Equivalent of #20226, but for TTree::Draw. In this case it's slightly more difficult to trigger the integer overflow, albeit absolutely doable. a run of the reproducer shows an empty histogram, thus confirming that the overflow prevents the loop from even starting. This is due to (in the case nentries==TTree::kMaxEntries)

root/tree/treeplayer/src/TTreePlayer.cxx

Line 2294 in a1c112f

for (entry=firstentry;entry<firstentry+nentries;entry++) {

Guarded by this innocent-looking line

root/tree/treeplayer/src/TTreePlayer.cxx

Lines 429 to 430 in a1c112f

	// Do not process more than fMaxEntryLoop entries
	if (nentries > fTree->GetMaxEntryLoop()) nentries = fTree->GetMaxEntryLoop();

Reproducer

#include <TChain.h>
#include <TFile.h>
#include <TTree.h>

#include <memory>
#include <iostream>

void make_step_one_file(const char *name, const char *treename, int nEntries)
{
    auto file = std::make_unique<TFile>(name, "RECREATE");
    auto tree = std::make_unique<TTree>(treename, treename);

    for (int i = 0; i < nEntries; ++i)
    {
        tree->Fill();
    }

    file->Write();
}

void make_step_zero_file(const char *name, const char *treename, int first, int last)
{
    auto file = std::make_unique<TFile>(name, "RECREATE");
    auto tree = std::make_unique<TTree>(treename, treename);

    int index{};
    int value{};
    tree->Branch("index", &index);
    tree->Branch("value", &value);

    for (index = first; index < last; ++index)
    {
        value = 2 * index;
        tree->Fill();
    }

    file->Write();
}

void ttree_scan_int_overflow()
{
    make_step_zero_file("friends-hybrid-step0-0.root", "stepzerotree", 0, 10);
    auto file = std::make_unique<TFile>("friends-hybrid-step0-0.root");
    std::unique_ptr<TTree> tree{file->Get<TTree>("stepzerotree")};

    tree->SetMaxEntryLoop(TTree::kMaxEntries);

    std::cout << tree->Draw("index", "", "", TTree::kMaxEntries, 3) << "\n";
}

int main()
{
    ttree_scan_int_overflow();
}

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