From fc1cf5033c999922478372007cdc0793a9aaeb2a Mon Sep 17 00:00:00 2001
From: Willem Deconinck <willem.deconinck@ecmwf.int>
Date: Fri, 22 Nov 2024 10:07:46 +0100
Subject: [PATCH] bugfix: DIV_BY_ZERO in
 MatchingFunctionSpacePartitionerLonLatPolygon for small grids with OMP (#244)

---
 .../MatchingFunctionSpacePartitionerLonLatPolygon.cc           | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/atlas/grid/detail/partitioner/MatchingFunctionSpacePartitionerLonLatPolygon.cc b/src/atlas/grid/detail/partitioner/MatchingFunctionSpacePartitionerLonLatPolygon.cc
index c202b11dd..03b99b6df 100644
--- a/src/atlas/grid/detail/partitioner/MatchingFunctionSpacePartitionerLonLatPolygon.cc
+++ b/src/atlas/grid/detail/partitioner/MatchingFunctionSpacePartitionerLonLatPolygon.cc
@@ -56,6 +56,9 @@ void MatchingFunctionSpacePartitionerLonLatPolygon::partition(const Grid& grid,
             ATLAS_TRACE("point-in-polygon check for entire grid (" + std::to_string(grid.size()) + " points)");
             size_t num_threads = atlas_omp_get_max_threads();
             size_t chunk_size  = grid.size() / (1000 * num_threads);
+            if (chunk_size == 0) {
+                chunk_size = grid.size();
+            }
             size_t chunks      = num_threads == 1 ? 1 : std::max(size_t(1), size_t(grid.size()) / chunk_size);
             atlas_omp_pragma(omp parallel for schedule(dynamic,1))
             for( size_t chunk=0; chunk < chunks; ++chunk) {