From: Martin Kronbichler <martin.kronbichler@uni-a.de>
Date: Sun, 26 Jun 2022 06:38:34 +0000 (+0200)
Subject: Small improvement for IndexSet::add_ranges_internal
X-Git-Tag: v9.5.0-rc1~1149^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F14052%2Fhead;p=dealii.git

Small improvement for IndexSet::add_ranges_internal
---

diff --git a/source/base/index_set.cc b/source/base/index_set.cc
index 7b5960fe3f..1a47ae2c01 100644
--- a/source/base/index_set.cc
+++ b/source/base/index_set.cc
@@ -415,7 +415,17 @@ IndexSet::add_ranges_internal(
       tmp_set.ranges.reserve(tmp_ranges.size());
       for (const auto &i : tmp_ranges)
         tmp_set.add_range(i.first, i.second);
-      this->add_indices(tmp_set);
+
+      // Case if we have zero or just one range: Add into the other set with
+      // its indices, as that is cheaper
+      if (this->ranges.size() <= 1)
+        {
+          if (this->ranges.size() == 1)
+            tmp_set.add_range(ranges[0].begin, ranges[0].end);
+          std::swap(*this, tmp_set);
+        }
+      else
+        this->add_indices(tmp_set);
     }
   else
     for (const auto &i : tmp_ranges)