From af2e5c8b1bf17a0a0e1c1492735395bdd49ffd65 Mon Sep 17 00:00:00 2001
From: Mattias Ellert <mattias.ellert@physics.uu.se>
Date: Mon, 29 Jun 2020 12:57:43 +0200
Subject: [PATCH] Fix off-by-one error in the histogram v7 bin iterator

The histogram bin iterator should start at 1 and end at N + 1, not
start at 0 and end at N. (As for all iterators, the end element is the
invalid element after the last one.)

Fixes an assertion in the histhistv7testUnit test

[----------] 2 tests from BinIterNBins
[ RUN      ] BinIterNBins.NumBins
/usr/include/c++/10/bits/stl_vector.h:1045: std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](std::vector<_Tp, _Alloc>::size_type) [with _Tp = float; _Alloc = std::allocator<float>; std::vector<_Tp, _Alloc>::reference = float&; std::vector<_Tp, _Alloc>::size_type = long unsigned int]: Assertion '__builtin_expect(__n < this->size(), true)' failed.
---
 hist/histv7/inc/ROOT/RHist.hxx | 4 ++--
 hist/histv7/test/biniter.cxx   | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/hist/histv7/inc/ROOT/RHist.hxx b/hist/histv7/inc/ROOT/RHist.hxx
index ebb319f1ef..9521fe182f 100644
--- a/hist/histv7/inc/ROOT/RHist.hxx
+++ b/hist/histv7/inc/ROOT/RHist.hxx
@@ -158,9 +158,9 @@ public:
    /// Get the uncertainty on the content of the bin at `x`.
    double GetBinUncertainty(const CoordArray_t &x) const { return fImpl->GetBinUncertainty(x); }
 
-   const_iterator begin() const { return const_iterator(*fImpl); }
+   const_iterator begin() const { return const_iterator(*fImpl, 1); }
 
-   const_iterator end() const { return const_iterator(*fImpl, fImpl->GetNBinsNoOver()); }
+   const_iterator end() const { return const_iterator(*fImpl, fImpl->GetNBinsNoOver() + 1); }
 
    /// Swap *this and other.
    ///
diff --git a/hist/histv7/test/biniter.cxx b/hist/histv7/test/biniter.cxx
index aa1c2dfef9..1f940aa8e7 100644
--- a/hist/histv7/test/biniter.cxx
+++ b/hist/histv7/test/biniter.cxx
@@ -45,7 +45,7 @@ TEST(BinIterNBins, BinRef) {
   double founduncert = -1.;
   RH2F::CoordArray_t foundcoord{};
 
-  int nBins = 0;
+  int nBins = 1;
   for (auto bin: h) {
     auto binCenter = bin.GetCenter();
     if (std::fabs(binCenter[0] - x) < 0.1 && std::fabs(binCenter[1] - y) < 0.1) {
-- 
2.26.2